Fixing Travis error with node v0.8

Travis builds have been broken for a while, it seems **0.9.11** is the min required version for the tests to work.
(I incrementally tested from **0.8.0** to **0.9.11** to find the working min version)

I've consciously upped the min-node requirement to **0.9.11** as well to match the Travis config. my reasoning is there is no value in making backward compatible features with **0.8** at this point as many of the apis are broken and will require some significant workarounds to make work with **0.8**. an effort that seems wasteful in favour on working on optimization and stability.

if the community has a need for **0.8** then this would mean continuing to build workarounds, starting with the reason for this error in Travis, which is: 

`Warning: Object #<Object> has no method 'tmpdir' Use --force to continue.` in `test/core/resolvers/resolver.js:461`