Bump Gem version to 3.11.6
update AUTHORS.md
Bumps JWT again.
Updates rspec to v3. Removes Gemfile gems from gemspec.

The rspec syntax for the test was updated recently, but rspec itself wasn't bumped, so old installs would fail the tests.
Also, rspec, fakeweb and rack were all declared in both the Gemfile test group and as development dependencies in the gemspec. Whilst I'd rather have them as development dependencies, I noticed a commit from @karlfreeman that moved them to the Gemfile, so I will stick with this for the project. I have removed them again from the gemspec for consistency.
Merge pull request #98 from philnash/bump-jwt

Bump JWT version to 1.0
Merge pull request #99 from philnash/updates-rspec-version

Update RSpec to v3 and move test dependencies to Gemfile
Adds rack middleware for webhook authentication
Updates middleware failure status code to 403.
Updates the request validation middleware docs to say 403.
Merge pull request #100 from philnash/rack-middleware

Adds rack middleware for webhook authentication