fix a path issue when creating new flutter apps

packages/flutter_tools/lib/src/common.dart

@@ -14,7 +14,8 @@ abstract class CommandHandler {
 
   ArgParser get parser;
 
-  /// @return 0 for no errors or warnings executing command, 1 for warnings, 2 for errors.
+  /// Returns 0 for no errors or warnings executing command, 1 for warnings, 2
+  /// for errors.
   Future<int> processArgResults(ArgResults results);
 
   void printUsage([String message]) {

packages/flutter_tools/lib/src/init.dart

@@ -89,6 +89,7 @@ abstract class Template {
     files.forEach((String path, String contents) {
       Map m = {'projectName': projectName, 'description': description};
       contents = mustache.render(contents, m);
+      path = path.replaceAll('/', Platform.pathSeparator);
       File file = new File(p.join(dir.path, path));
       file.parent.createSync();
       file.writeAsStringSync(contents);