Loosen version requirements for faraday_middleware

Just to be sure I ran the specs against all the versions list here

![](http://f.cl.ly/items/3k2330283m151s2C0U18/Screen%20Shot%202013-03-19%20at%209.17.41%20AM.png)
Merge pull request #7 from arronmabrey/patch-1

Loosen version requirements for faraday_middleware