Update .travis.yml.

Author: 23Skidoo

.travis.yml

@@ -27,7 +27,7 @@ before_cache:
 matrix:
   include:
     - compiler: ghc-8.8.3
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.8.1","cabal-install-3.0"]}}
+      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.8.3","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