Update dependencies

 * closure-util@0.12.0 - force inclusion of deps.js files when compiling
 * jshint@2.5.1 - various enhancements and fixes (https://github.com/jshint/jshint/compare/2.4.4...2.5.1)
 * walk@2.3.3 - directory exclusion fix
Merge pull request #2099 from tschaub/update-deps

Update dependencies.