Please loosen faraday dependency to '~> 0.8' instead of ~> '0.8.0'

[asanghi]

Unless there is some specific reason for it, can you please loosen the dependency on faraday? Version 0.9 of faraday has been released recently.

[brodock]

Are you willing to accept any PR that makes sure this gem is compatible with either faraday 0.8.x and 0.9.x?