code: function (onFinally) {
              return this.then(function (val) {
                  return Yaku.resolve(onFinally()).then(function () {
                      return val;
                  });
              }, function (err) {
                  return Yaku.resolve(onFinally()).then(function () {
                      throw err;
                  });
              });
          }
docs: Register a callback to be invoked when a promise is settled (either fulfilled or rejected).
  Similar with the try-catch-finally, it's often used for cleanup.
  @param  {Function} onFinally A Function called when the Promise is settled.
  It will not receive any argument.
  @return {Yaku} A Promise that will reject if onFinally throws an error or returns a rejected promise.
  Else it will resolve previous promise's final state (either fulfilled or rejected).
  @example
  ```js
  var Promise = require('yaku');
  var p = Promise.reject(new Error("ERR"));
  
  p['catch']((v) => {
  console.log(v);
  });
  ```