function removeKeyword(keyword) {
        /* jshint validthis: true */
        var RULES = this.RULES
        delete RULES.keywords[keyword]
        delete RULES.all[keyword]
        delete RULES.custom[keyword]
        for (var i = 0; i < RULES.length; i++) {
          var rules = RULES[i].rules
          for (var j = 0; j < rules.length; j++) {
            if (rules[j].keyword == keyword) {
              rules.splice(j, 1)
              break
            }
          }
        }
        return this
      }
Create a base64 sha1 HMAC for `options`.

Specifically to be used with S3 presigned URLs

@param {Object} options
@return {String}
@api private