lib/lexer.js
function(regex) {
    var m = regex.exec(this.input);
    if (m) {
      this.updatePosition(m[0], m[0].length);
      return m;
    }
  }
function(regex) {
    var m = regex.exec(this.input);
    if (m) {
      this.updatePosition(m[0], m[0].length);
      return m;
    }
  }
Match `regex`, return captures, and update the cursor position by `match[0]` length.
@param {RegExp} `regex`
@return {Object}