Upgrading to Dart 2.8  (#497)

diff --git a/.travis.yml b/.travis.yml
index ac2723b..02275d3 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,7 +3,7 @@
   - gem install coveralls-lcov
 dart:
   # Keep this value aligned with min SDK value in pubspec.yaml and FROM line of Dockerfile
-  - "2.7.2"
+  - "2.8.1"
   - beta
 
 # Speed up builds by using containerization. Disable this if you need to use
diff --git a/Dockerfile b/Dockerfile
index b456c0d..4c9b343 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,5 +1,5 @@
 # Keep aligned with min SDK in pubspec.yaml and Dart test version in .travis.yml
-FROM google/dart:2.7.2
+FROM google/dart:2.8.1
 
 # The specific commit that dart-services should use. This should be kept
 # in sync with the flutter submodule in the dart-services repo.
diff --git a/example/pubspec.lock b/example/pubspec.lock
index 814fc22..c20cd7d 100644
--- a/example/pubspec.lock
+++ b/example/pubspec.lock
@@ -70,7 +70,7 @@
       name: build_modules
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.8.1"
+    version: "2.9.0"
   build_resolvers:
     dependency: transitive
     description:
@@ -98,7 +98,7 @@
       name: build_web_compilers
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.9.0"
+    version: "2.10.0"
   built_collection:
     dependency: transitive
     description:
@@ -450,4 +450,4 @@
     source: hosted
     version: "2.2.1"
 sdks:
-  dart: ">=2.7.0 <3.0.0"
+  dart: ">=2.8.1 <3.0.0"
diff --git a/example/pubspec.yaml b/example/pubspec.yaml
index 5fc9a66..b08888c 100644
--- a/example/pubspec.yaml
+++ b/example/pubspec.yaml
@@ -3,7 +3,7 @@
 version: 1.0.0
 
 environment:
-  sdk: '>=2.7.0 <3.0.0'
+  sdk: ^2.8.1
 
 dependencies:
   codemirror: ^0.5.15
@@ -11,5 +11,5 @@
 
 dev_dependencies:
   build_runner: ^1.8.1
-  build_web_compilers: ^2.9.0
+  build_web_compilers: ^2.10.0
   pedantic: ^1.9.0
diff --git a/pubspec.lock b/pubspec.lock
index cfc9828..2bf9792 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -203,7 +203,7 @@
       name: dartis
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.4.0"
+    version: "0.5.0"
   fixnum:
     dependency: transitive
     description:
@@ -653,4 +653,4 @@
     source: hosted
     version: "2.2.1"
 sdks:
-  dart: ">=2.7.2 <3.0.0"
+  dart: ">=2.8.1 <3.0.0"
diff --git a/pubspec.yaml b/pubspec.yaml
index 14dcfbd..895fd96 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -3,7 +3,7 @@
 
 environment:
   # Keep SDK aligned with .travis.yml and FROM line of Dockerfile
-  sdk: ^2.7.2
+  sdk: ^2.8.1
 
 dependencies:
   analyzer: ^0.39.0
@@ -12,7 +12,7 @@
   args: ^1.5.2
   bazel_worker: ^0.1.23
   crypto: ^2.0.0
-  dartis: ^0.4.0
+  dartis: ^0.5.0
   http: ^0.12.0
   logging: ^0.11.0
   meta: ^1.1.8