Fix escaping in YAML RegExp.

This was causing it to try to parse "m4" as a number, which fails.
Fixes dart-lang/yaml#9128.
BUG=

Review URL: https://codereview.chromium.org//12876003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/yaml@20107 260f80e4-7a28-3924-810f-c04153c831b5
1 file changed
tree: 90d125b1799f84e8d950d9eb58009272889de348
  1. pkgs/