Update .travis.yml

Re-enable ghcjs in Travis  (now that time limit is 90 minutes)

Author: oliver-batchelor

.travis.yml

@@ -39,9 +39,7 @@ matrix:
       addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.2.2","cabal-install-2.4"]}}
     - compiler: ghc-8.0.2
       addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.0.2","cabal-install-2.4"]}}
-  allow_failures:
-    - compiler: "ghcjs-8.4" # This hits the travis 50min time limit and fails
-
+  
 before_install:
   - |
     if [ "$TRAVIS_OS_NAME" = "linux" ] && [ ! -z "$GHCJS_PACKAGE" ]; then