Add travis build with ghc-8.0.1

Author: qnikst

.travis.yml

@@ -10,6 +10,8 @@ matrix:
       addons: {apt: {packages: [cabal-install-1.22,ghc-7.8.4], sources: [hvr-ghc]}}
     - env: CABALVER=1.22 GHCVER=7.10.3
       addons: {apt: {packages: [cabal-install-1.22,ghc-7.10.3],sources: [hvr-ghc]}}
+    - env: CABALVER=1.24 GHCVER=8.0.1
+      addons: {apt: {packages: [cabal-install-1.24,ghc-8.0.1], sources: [hvr-ghc]}}
 
 before_install:
   - export PATH=/opt/ghc/$GHCVER/bin:/opt/cabal/$CABALVER/bin:~/.cabal/bin:$PATH