Factor out haskell-ci configuration

.travis.yml

@@ -186,5 +186,5 @@ script:
   # haddock
   - if $HADDOCK; then cabal new-haddock -w ${HC} ${TEST} ${BENCH} all; else echo "Skipping haddock generation";fi
 
-# REGENDATA ["-o",".travis.yml","--ghc-head","--no-unconstrained","cabal.project"]
+# REGENDATA ["--output=.travis.yml","--config=cabal.haskell-ci","cabal.project"]
 # EOF

cabal.haskell-ci

+ghc-head:      True
+unconstrained: False