fixing travis.

Author: kazu-yamamoto

.travis.yml

@@ -40,7 +40,7 @@ matrix:
       addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.4,ghc-8.6.5], sources: [hvr-ghc]}}
     - compiler: "ghc-8.8.3"
     # env: TEST=--disable-tests BENCH=--disable-benchmarks
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-3.0,ghc-8.8.1], sources: [hvr-ghc]}}
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-3.0,ghc-8.8.3], sources: [hvr-ghc]}}
     - compiler: "ghc-head"
     # env: TEST=--disable-tests BENCH=--disable-benchmarks
       addons: {apt: {packages: [ghc-ppa-tools,cabal-install-head,ghc-head], sources: [hvr-ghc]}}