migrate raw string to new syntax in pkg

pkg/args/lib/args.dart

 // Copyright (c) 2012, 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.
 
 /**
  * This library lets you define parsers for parsing raw command-line arguments
  * into a set of options and values using [GNU][] and [POSIX][] style options.
  *
  * ## Defining options ##
  *
@@ skipping 177 matching lines @@
 #import('dart:math');
 
 // TODO(rnystrom): Use "package:" URL here when test.dart can handle pub.
 #import('src/utils.dart');
 
 /**
  * A class for taking a list of raw command line arguments and parsing out
  * options and flags from them.
  */
 class ArgParser {
-  static const _SOLO_OPT = const RegExp(@'^-([a-zA-Z0-9])$');
-  static const _ABBR_OPT = const RegExp(@'^-([a-zA-Z0-9]+)(.*)$');
-  static const _LONG_OPT = const RegExp(@'^--([a-zA-Z\-_0-9]+)(=(.*))?$');
+  static const _SOLO_OPT = const RegExp(r'^-([a-zA-Z0-9])$');
+  static const _ABBR_OPT = const RegExp(r'^-([a-zA-Z0-9]+)(.*)$');
+  static const _LONG_OPT = const RegExp(r'^--([a-zA-Z\-_0-9]+)(=(.*))?$');
 
   final Map<String, _Option> _options;
 
   /**
    * The names of the options, in the order that they were added. This way we
    * can generate usage information in the same order.
    */
   // TODO(rnystrom): Use an ordered map type, if one appears.
   final List<String> _optionNames;
 
@@ skipping 560 matching lines @@
       allowedBuffer.add(allowed);
       if (allowed == option.defaultValue) {
         allowedBuffer.add(' (default)');
       }
       first = false;
     }
     allowedBuffer.add(']');
     return allowedBuffer.toString();
   }
 }