style(dart/transform): Change quote character for consistency.

Use ' as a quote character in generated output instead of ".

modules/angular2/src/transform/directive_processor/rewriter.dart

@@ -150,19 +150,19 @@ class CreateNgDepsVisitor extends Object
       }
       writer.print('..registerType(');
       visitNode(node.name);
-      writer.print(', {"factory": ');
+      writer.print(', {\'factory\': ');
       if (ctor == null) {
         _generateEmptyFactory(node.name.toString());
       } else {
         ctor.accept(_factoryVisitor);
       }
-      writer.print(', "parameters": ');
+      writer.print(', \'parameters\': ');
       if (ctor == null) {
         _generateEmptyParams();
       } else {
         ctor.accept(_paramsVisitor);
       }
-      writer.print(', "annotations": ');
+      writer.print(', \'annotations\': ');
       node.accept(_metaVisitor);
       writer.print('})');