Correct markdown in library dartdoc
This dartdoc has "code" examples that are not rendered as code. This change fixes that.
diff --git a/lib/source_maps.dart b/lib/source_maps.dart
index 0d17178..0c6cc08 100644
--- a/lib/source_maps.dart
+++ b/lib/source_maps.dart
@@ -5,19 +5,25 @@
/// Library to create and parse source maps.
///
/// Create a source map using [SourceMapBuilder]. For example:
-/// var json = (new SourceMapBuilder()
-/// ..add(inputSpan1, outputSpan1)
-/// ..add(inputSpan2, outputSpan2)
-/// ..add(inputSpan3, outputSpan3)
-/// .toJson(outputFile);
+///
+/// ```dart
+/// var json = (new SourceMapBuilder()
+/// ..add(inputSpan1, outputSpan1)
+/// ..add(inputSpan2, outputSpan2)
+/// ..add(inputSpan3, outputSpan3)
+/// .toJson(outputFile);
+/// ```
///
/// Use the source_span package's [SourceSpan] and [SourceFile] classes to
/// specify span locations.
///
/// Parse a source map using [parse], and call `spanFor` on the returned mapping
/// object. For example:
-/// var mapping = parse(json);
-/// mapping.spanFor(outputSpan1.line, outputSpan1.column)
+///
+/// ```dart
+/// var mapping = parse(json);
+/// mapping.spanFor(outputSpan1.line, outputSpan1.column)
+/// ```
library source_maps;
import 'package:source_span/source_span.dart';
