Update #respond_to matcher with 2.1.0 required keyword arguments.

Current spec status:
  1.9.3: 317 examples, 0 failures in 0.12658 seconds.
  2.0.0: 332 examples, 0 failures in 0.13776 seconds.
  2.1.0: 346 examples, 0 failures in 0.11231 seconds.
Update #construct matcher with 2.1.0 required keywords.

Current spec status:
  1.9.3: 317 examples, 0 failures in 0.1256 seconds.
  2.0.0: 332 examples, 0 failures in 0.13982 seconds.
  2.1.0: 355 examples, 0 failures in 0.11697 seconds.
Merge pull request #1 from sleepingkingstudios/feature-required-keywords

Update matchers with 2.1.0 required keywords.