style(dart/transform): Rename .ngDeps.dart => .ng_deps.dart

Update to conform with file naming conventions.

Closes #975

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

@@ -31,7 +31,7 @@ String createNgDeps(String code, String path, {bool forceGenerate: false}) {
 }
 
 /// Visitor responsible for processing [CompilationUnit] and creating an
-/// associated .ngDeps.dart file.
+/// associated .ng_deps.dart file.
 class CreateNgDepsVisitor extends Object
     with SimpleAstVisitor<Object>, VisitorMixin {
   final PrintWriter writer;

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

@@ -11,10 +11,10 @@ import 'package:barback/barback.dart';
 import 'rewriter.dart';
 
 /// Transformer responsible for processing all .dart assets and creating
-/// .ngDeps.dart files which register @Injectable annotated classes with the
+/// .ng_deps.dart files which register @Injectable annotated classes with the
 /// reflector.
 ///
-/// This will also create .ngDeps.dart files for classes annotated
+/// This will also create .ng_deps.dart files for classes annotated
 /// with @Component, @Template, @Decorator, etc.
 ///
 /// This transformer is the first phase in a two-phase transform. It should