Allow Faraday to follow redirects

[wwboynton]

Apparently some BitBucket endpoints will serve a 302 redirect. This was causing an error.

For example:

irb(main):035:0> pp b.pull_requests.diff('my_user', 'my_repo', '1')
RuntimeError: can't modify frozen NilClass
	from /Users/wboynton/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/bitbucket_rest_api-0.1.7/lib/bitbucket_rest_api/response/helpers.rb:17:in `block in on_complete'
	from /Users/wboynton/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/bitbucket_rest_api-0.1.7/lib/bitbucket_rest_api/response/helpers.rb:17:in `instance_eval'
	from /Users/wboynton/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/bitbucket_rest_api-0.1.7/lib/bitbucket_rest_api/response/helpers.rb:17:in `on_complete'
	from /Users/wboynton/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/faraday-0.9.2/lib/faraday/response.rb:9:in `block in call'
	from /Users/wboynton/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/faraday-0.9.2/lib/faraday/response.rb:57:in `on_complete'
	from /Users/wboynton/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/faraday-0.9.2/lib/faraday/response.rb:8:in `call'
	from /Users/wboynton/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/faraday_middleware-0.9.2/lib/faraday_middleware/request/encode_json.rb:23:in `call'
	from /Users/wboynton/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/bitbucket_rest_api-0.1.7/lib/bitbucket_rest_api/request/basic_auth.rb:14:in `call'
	from /Users/wboynton/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/faraday-0.9.2/lib/faraday/request/url_encoded.rb:15:in `call'
	from /Users/wboynton/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/faraday-0.9.2/lib/faraday/request/multipart.rb:14:in `call'
	from /Users/wboynton/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/faraday-0.9.2/lib/faraday/rack_builder.rb:139:in `build_response'
	from /Users/wboynton/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/faraday-0.9.2/lib/faraday/connection.rb:377:in `run_request'
	from /Users/wboynton/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/faraday-0.9.2/lib/faraday/connection.rb:140:in `get'
	from /Users/wboynton/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/bitbucket_rest_api-0.1.7/lib/bitbucket_rest_api/request.rb:42:in `request'
	from /Users/wboynton/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/bitbucket_rest_api-0.1.7/lib/bitbucket_rest_api/repos/pull_request.rb:100:in `diff'
	from (irb):35
	from /Users/wboynton/.rbenv/versions/2.4.1/bin/irb:11:in `<main>'

Following the directions from this Faraday issue, it seemed like all I needed to do was use the FaradayMiddleware::FollowRedirects and explicitly mount an adapter. I did that and the same code began working. You can scrutinize and change this at your leisure, but GET-ting data from (at least) that endpoint will be broken until Faraday is using redirects.

[wwboynton]

Note, this does not solve the issue that follows that -- the /diff endpoint sends a non-JSON response body, which fails in /response/jsonize.rb. I wasn't sure of the most appropriate way to deal with that in context of the whole library, so I'm patching it for myself and leave you to determine how non-JSON bodies should be handled.