Update ruby-faraday to 0.12.1.

Faraday 0.12.1 2017/04/21

* Fix an issue with Patron tests failing on jruby
* Fix an issue with new rewind_files feature that was causing an exception
  when the body was not an Hash
* Expose wrapped_exception in all client errors
* Add Authentication Section to the ReadMe

Faraday 0.12.0.1 2017/04/02

*Hotfix release to address an issue with TravisCI deploy on Rubygems

Faraday 0.12.0 2017/03/21

* Proxy feature now relies on Ruby URI::Generic#find_proxy and can use
  no_proxy ENV variable (not compatible with ruby < 2.0)
* Fix an issue with options that was causing new options to override defaults
  ones unexpectedly
* Rewind UploadIOs on retry to fix a compatibility issue
* Make multipart boundary unique
* Adds support for context request option to pass arbitrary information to
  middlewares
* Improvements in README.md

(taca)