Exclude GHC < 7.6 because of build failure
Exclude GHC < 7.6 because of build failure

```
src/Hi.hs:12:8:
    Could not find module `GHC.Generics'
    It is a member of the hidden package `ghc-prim'.
    Perhaps you need to add `ghc-prim' to the build-depends in your .cabal file.
    Use -v to see a list of the files searched for.
```
ndmitchell/weeder