Fix analysis issues (dart-archive/stack_trace#160)

Author: osa1

pkgs/stack_trace/lib/src/frame.dart

@@ -218,9 +218,12 @@ class Frame {
 
   /// Parses a Firefox 'eval' or 'function' stack frame.
   ///
-  /// for example:
+  /// For example:
+  ///
+  /// ```
   /// anonymous/<@https://example.com/stuff.js line 693 > Function:3:40
   /// anonymous/<@https://example.com/stuff.js line 693 > eval:3:40
+  /// ```
   factory Frame._parseFirefoxEval(String frame) =>
       _catchFormatException(frame, () {
         final match = _firefoxEvalLocation.firstMatch(frame);

pkgs/stack_trace/lib/src/trace.dart

@@ -31,9 +31,12 @@ final _v8TraceLine = RegExp(r'    ?at ');
 ///
 /// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/stack
 ///
-/// These stack traces looks like:
-///     anonymous/<@https://example.com/stuff.js line 693 > Function:3:40
-///     anonymous/<@https://example.com/stuff.js line 693 > eval:3:40
+/// These stack traces look like:
+///
+/// ````
+/// anonymous/<@https://example.com/stuff.js line 693 > Function:3:40
+/// anonymous/<@https://example.com/stuff.js line 693 > eval:3:40
+/// ````
 final _firefoxEvalTrace = RegExp(r'@\S+ line \d+ >.* (Function|eval):\d+:\d+');
 
 /// A RegExp to match Firefox and Safari's stack traces.