Constrained Happstack version in builds with older dependency versions

Author: sebright

.travis.yml

@@ -61,6 +61,10 @@ before_install:
       echo "constraints:aeson=="$AESONVER >> cabal.config;
    fi
 
+   if [[ $HPVER == 2012.* ]]; then
+      echo "constraints:happstack-server==7.3.0" >> cabal.config;
+   fi
+
  - sudo add-apt-repository -y ppa:hvr/ghc
  - sudo apt-get update
  - sudo apt-get install cabal-install-1.18 ghc-$GHCVER