Change dependency on base to <4.8

It seems that the current dependency of >=4.6 && <4.7 doesn't build on
GHC 7.8.2.

hapistrano.cabal

@@ -16,7 +16,7 @@ executable hap
   main-is:             Main.hs
   -- other-modules:
   -- other-extensions:
-  build-depends:         base >=4.6 && <4.7
+  build-depends:         base >=4.6 && <4.8
                        , time
                        , old-locale
                        , process
@@ -24,4 +24,4 @@ executable hap
                        , transformers
                        , lens >= 4.1
   hs-source-dirs:      src
-  default-language:    Haskell2010
+  default-language:    Haskell2010