Fix a message bug.

lib/src/span_mixin.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:math' as math;
 import 'package:path/path.dart' as p;
 
 import 'colors.dart' as colors;
 import 'span.dart';
 import 'span_with_context.dart';
@@ skipping 52 matching lines @@
     var textLine;
     if (this is SourceSpanWithContext) {
       var context = (this as SourceSpanWithContext).context;
       var lineStart = findLineStart(context, text, column);
       if (lineStart != null && lineStart > 0) {
         buffer.write(context.substring(0, lineStart));
         context = context.substring(lineStart);
       }
       var endIndex = context.indexOf('\n');
       textLine = endIndex == -1 ? context : context.substring(0, endIndex + 1);
-      column = math.min(column, textLine.length - 1);
+      column = math.min(column, textLine.length);
     } else {
       textLine = text.split("\n").first;
       column = 0;
     }
 
     var toColumn =
         math.min(column + end.offset - start.offset, textLine.length);
     if (color != null) {
       buffer.write(textLine.substring(0, column));
       buffer.write(color);
@@ skipping 11 matching lines @@
     return buffer.toString();
   }
 
   bool operator ==(other) => other is SourceSpan &&
       start == other.start && end == other.end;
 
   int get hashCode => start.hashCode + (31 * end.hashCode);
 
   String toString() => '<$runtimeType: from $start to $end "$text">';
 }