only build on ghc 8.8.1 for testing travis out, move arrayfire install to install stanza

Author: chessai

.travis.yml

@@ -29,18 +29,13 @@ matrix:
   include:
     - compiler: ghc-8.8.1
       addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.8.1","cabal-install-3.0"]}}
-    - compiler: ghc-8.6.5
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.6.5","cabal-install-2.4"]}}
-    - compiler: ghc-8.4.4
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.4.4","cabal-install-2.4"]}}
-    - compiler: ghc-8.2.2
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.2.2","cabal-install-2.4"]}}
+    #- compiler: ghc-8.6.5
+    #  addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.6.5","cabal-install-2.4"]}}
+    #- compiler: ghc-8.4.4
+    #  addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.4.4","cabal-install-2.4"]}}
+    #- compiler: ghc-8.2.2
+    #  addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.2.2","cabal-install-2.4"]}}
 before_install:
-  - echo 'Downloading arrayfire-3.6.4'  
-  - curl -O http://arrayfire.s3.amazonaws.com/3.6.4/ArrayFire-v3.6.4_Linux_x86_64.sh
-  - chmod +x ArrayFire-v3.6.4_Linux_x86_64.sh
-  - ./ArrayFire-v3.6.4_Linux_x86_64.sh --include-subdir --prefix=/opt
-  - ls -lah /opt/arrayfire/
   - HC=$(echo "/opt/$CC/bin/ghc" | sed 's/-/\//')
   - WITHCOMPILER="-w $HC"
   - HCPKG="$HC-pkg"
@@ -72,6 +67,11 @@ before_install:
     }
   - echo text | color_cabal_output
 install:
+  - echo "Downloading ArrayFire-3.6.4" 
+  - curl -O http://arrayfire.s3.amazonaws.com/3.6.4/ArrayFire-v3.6.4_Linux_x86_64.sh
+  - chmod +x ArrayFire-v3.6.4_Linux_x86_64.sh
+  - ./ArrayFire-v3.6.4_Linux_x86_64.sh --include-subdir --prefix=/opt
+  - ls -lah /opt/arrayfire/
   - ${CABAL} --version
   - echo "$(${HC} --version) [$(${HC} --print-project-git-commit-id 2> /dev/null || echo '?')]"
   - TEST=--enable-tests