tweak the ghc travis matrix

Author: cartazio

.travis.yml

@@ -29,7 +29,7 @@ before_cache:
 matrix:
   include:
     - compiler: "ghc-8.6.2"
-      env: GHCHEAD=true TESTTARGETS="vector:vector-tests-O0" # https://ghc.haskell.org/trac/ghc/ticket/13535
+      env: TESTTARGETS="vector:vector-tests-O0" # https://ghc.haskell.org/trac/ghc/ticket/13535
       addons: {apt: {packages: [ghc-ppa-tools,cabal-install-head,ghc-8.6.1], sources: [hvr-ghc]}}
     - compiler: "ghc-8.4.3"
       env: TESTTARGETS="vector:vector-tests-O0" # https://ghc.haskell.org/trac/ghc/ticket/13535
@@ -58,7 +58,6 @@ matrix:
 
   allow_failures:
     - compiler: "ghc-head"
-    - compiler: "ghc-8.6.1"
 
 before_install:
   - HC=${CC}