eliminate analyzer warnings

pkgs/markdown/bin/markdown.dart

diff --git a/pkgs/markdown/bin/markdown.dart b/pkgs/markdown/bin/markdown.dart
index f6932ec..76f68e1 100644
--- a/pkgs/markdown/bin/markdown.dart
+++ b/pkgs/markdown/bin/markdown.dart
@@ -2,7 +2,7 @@
 
 import 'package:markdown/markdown.dart';
 
-void main(List<String> args) async {
+main(List<String> args) async {
   if (args.length > 1) {
     print('Usage: markdown.dart [file]');
     exit(1);

pkgs/markdown/lib/src/html_renderer.dart

diff --git a/pkgs/markdown/lib/src/html_renderer.dart b/pkgs/markdown/lib/src/html_renderer.dart
index d9f8111..184f9f9 100644
--- a/pkgs/markdown/lib/src/html_renderer.dart
+++ b/pkgs/markdown/lib/src/html_renderer.dart
@@ -7,6 +7,7 @@
 import 'dart:collection';
 
 import 'ast.dart';
+import 'block_parser.dart';
 import 'document.dart';
 import 'extension_set.dart';
 import 'inline_parser.dart';

pkgs/markdown/lib/src/inline_parser.dart

diff --git a/pkgs/markdown/lib/src/inline_parser.dart b/pkgs/markdown/lib/src/inline_parser.dart
index afa9d37..ccdfa98 100644
--- a/pkgs/markdown/lib/src/inline_parser.dart
+++ b/pkgs/markdown/lib/src/inline_parser.dart
@@ -208,8 +208,6 @@
 
 /// Escape punctuation preceded by a backslash.
 class EscapeSyntax extends InlineSyntax {
-  final String substitute;
-
   EscapeSyntax() : super(r'''\\[!"#$%&'()*+,\-./:;<=>?@\[\\\]^_`{|}~]''');
 
   bool onMatch(InlineParser parser, Match match) {