Include GHC-8.0.1 in travis build

.travis.yml

@@ -13,12 +13,12 @@ before_cache:
 
 matrix:
   include:
-    - env: CABALVER=1.18 GHCVER=7.8.4
-      compiler: ": #GHC 7.8.4"
-      addons: {apt: {packages: [cabal-install-1.18,ghc-7.8.4], sources: [hvr-ghc]}}
-    - env: CABALVER=1.22 GHCVER=7.10.2
-      compiler: ": #GHC 7.10.2"
-      addons: {apt: {packages: [cabal-install-1.22,ghc-7.10.2], sources: [hvr-ghc]}}
+    - env: CABALVER=1.22 GHCVER=7.10.3
+      compiler: ": #GHC 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
+      compiler: ": #GHC 8.0.1"
+      addons: {apt: {packages: [cabal-install-1.24,ghc-8.0.1], sources: [hvr-ghc]}}
 
 before_install:
  - unset CC
@@ -38,7 +38,7 @@ install:
  - sed -i -e '1,/^Resolving /d' installplan.txt; cat installplan.txt
 
 # check whether current requested install-plan matches cached package-db snapshot
- - if diff -u installplan.txt $HOME/.cabsnap/installplan.txt;
+ - if diff -u $HOME/.cabsnap/installplan.txt installplan.txt;
    then
      echo "cabal build-cache HIT";
      rm -rfv .ghc;
@@ -50,7 +50,7 @@ install:
      mkdir -p $HOME/.ghc $HOME/.cabal/lib $HOME/.cabal/share $HOME/.cabal/bin;
      cabal install --only-dependencies --enable-tests --enable-benchmarks;
    fi
- 
+
 # snapshot package-db on cache miss
  - if [ ! -d $HOME/.cabsnap ];
    then