parse(context, depth=3) {
    var match   = context.match(/([0-9.]+)/gm);
    var version = (match && match[0]);
    if (version) {
      // force valid format: eg: 1.0 => 1.0.0 (with depth=3)
      var splited = version.split('.');
      for (var i = 0; i < depth; i++) {
        splited[i] = splited[i] || '0';
      }
      version = splited.join('.');
      version = lazy.semver.clean(version);
    }
    return version;
  }
parse version from string
@param  {String}      context   context contents version
@return {String|Null}           parsed version