Update example and necessary dependencies (#373)

diff --git a/example/app.dart b/example/app.dart
index b735ef8..ace4fa3 100644
--- a/example/app.dart
+++ b/example/app.dart
@@ -17,7 +17,7 @@
 final introText = r'''Markdown is the **best**!
 
 * It has lists.
-* It has [links](http://dart.dev).
+* It has [links](https://dart.dev).
 * It has _so much more_...''';
 
 // Flavor support.
@@ -67,7 +67,7 @@
 
   for (var block in htmlDiv.querySelectorAll('pre code')) {
     try {
-      highlightBlock(block);
+      highlightElement(block);
     } catch (e) {
       window.console.error('Error highlighting markdown:');
       window.console.error(e);
diff --git a/example/favicon.ico b/example/favicon.ico
deleted file mode 100644
index 7ba349b..0000000
--- a/example/favicon.ico
+++ /dev/null
Binary files differ
diff --git a/example/favicon.png b/example/favicon.png
new file mode 100644
index 0000000..43d2ffa
--- /dev/null
+++ b/example/favicon.png
Binary files differ
diff --git a/example/highlight.dart b/example/highlight.dart
index 29c699f..5dea80d 100644
--- a/example/highlight.dart
+++ b/example/highlight.dart
@@ -8,4 +8,4 @@
 import 'package:js/js.dart';
 
 @JS()
-external void highlightBlock(Object block);
+external void highlightElement(Object block);
diff --git a/example/index.html b/example/index.html
index f3da846..ba9d207 100644
--- a/example/index.html
+++ b/example/index.html
@@ -1,11 +1,12 @@
 <html>
   <head>
+    <link rel="icon" sizes="64x64" href="favicon.png">
     <link rel="stylesheet" href="style.css">
     <link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Roboto+Mono|Roboto">
     <link rel="stylesheet" href="https://fonts.googleapis.com/icon?family=Material+Icons+Extended">
-    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.8.0/styles/default.min.css">
-    <script defer src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.8.0/highlight.min.js"></script>
-    <script defer src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.8.0/languages/dart.min.js"></script>
+    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.0.1/styles/default.min.css">
+    <script defer src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.0.1/highlight.min.js"></script>
+    <script defer src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.0.1/languages/dart.min.js"></script>
     <script defer src="app.dart.js"></script>
     <title>Dart Markdown Live Editor</title>
   </head>
@@ -17,8 +18,8 @@
           <span style="display: flex; flex: 1;"></span>
           <span class="version"></span>
           <a href="https://github.com/dart-lang/markdown" title="Open Source on GitHub">
-            <svg class="octicon" height="32" version="1.1" viewBox="0 0 16 16" width="32">
-              <path d="M8 0C3.58 0 0 3.58 0 8c0 3.54 2.29 6.53 5.47 7.59.4.07.55-.17.55-.38 0-.19-.01-.82-.01-1.49-2.01.37-2.53-.49-2.69-.94-.09-.23-.48-.94-.82-1.13-.28-.15-.68-.52-.01-.53.63-.01 1.08.58 1.23.82.72 1.21 1.87.87 2.33.66.07-.52.28-.87.51-1.07-1.78-.2-3.64-.89-3.64-3.95 0-.87.31-1.59.82-2.15-.08-.2-.36-1.02.08-2.12 0 0 .67-.21 2.2.82.64-.18 1.32-.27 2-.27.68 0 1.36.09 2 .27 1.53-1.04 2.2-.82 2.2-.82.44 1.1.16 1.92.08 2.12.51.56.82 1.27.82 2.15 0 3.07-1.87 3.75-3.65 3.95.29.25.54.73.54 1.48 0 1.07-.01 1.93-.01 2.2 0 .21.15.46.55.38A8.013 8.013 0 0 0 16 8c0-4.42-3.58-8-8-8z"></path>
+            <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16" width="32" height="32">
+              <path fill-rule="evenodd" d="M8 0C3.58 0 0 3.58 0 8c0 3.54 2.29 6.53 5.47 7.59.4.07.55-.17.55-.38 0-.19-.01-.82-.01-1.49-2.01.37-2.53-.49-2.69-.94-.09-.23-.48-.94-.82-1.13-.28-.15-.68-.52-.01-.53.63-.01 1.08.58 1.23.82.72 1.21 1.87.87 2.33.66.07-.52.28-.87.51-1.07-1.78-.2-3.64-.89-3.64-3.95 0-.87.31-1.59.82-2.15-.08-.2-.36-1.02.08-2.12 0 0 .67-.21 2.2.82.64-.18 1.32-.27 2-.27.68 0 1.36.09 2 .27 1.53-1.04 2.2-.82 2.2-.82.44 1.1.16 1.92.08 2.12.51.56.82 1.27.82 2.15 0 3.07-1.87 3.75-3.65 3.95.29.25.54.73.54 1.48 0 1.07-.01 1.93-.01 2.2 0 .21.15.46.55.38A8.013 8.013 0 0016 8c0-4.42-3.58-8-8-8z"></path>
             </svg>
           </a>
         </div>
diff --git a/pubspec.yaml b/pubspec.yaml
index 4f55179..5a86fd5 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -17,11 +17,11 @@
   meta: ^1.3.0
 
 dev_dependencies:
-  build_runner: ^1.0.0
-  build_version: ^2.0.0
-  build_web_compilers: '>=1.0.0 <3.0.0'
+  build_runner: ^2.0.5
+  build_version: ^2.0.3
+  build_web_compilers: ^3.0.0
   collection: ^1.15.0
-  html: ^0.15.0-nullsafety
+  html: ^0.15.0
   io: ^1.0.0
   js: ^0.6.3
   lints: ^1.0.1
diff --git a/tool/update-gh-pages.sh b/tool/update-gh-pages.sh
index 64962a7..97762ad 100755
--- a/tool/update-gh-pages.sh
+++ b/tool/update-gh-pages.sh
@@ -4,7 +4,7 @@
 # Fail fast if a command fails.
 set -e
 
-pub global activate peanut
+dart pub global activate peanut
 
 peanut -d example