Only retry cabal test for the moment in travis config

Travis seems to have random network problems and their current recommended workaround is to retry a few times. I think we only want to do this for the tests (which is where we've seen the problems) and not for the main code compile check (where we'd end up getting the same build failure three times or whatever).

Author: dcoutts

.travis.yml

@@ -5,8 +5,8 @@ notifications:
   irc: "chat.freenode.net#hackage"
 
 install:
-  - travis_retry sudo apt-get install libicu-dev
-  - travis_retry cabal install --only-dependencies --enable-tests --disable-optimization --ghc-options=-w
+  - sudo apt-get install libicu-dev
+  - cabal install --only-dependencies --enable-tests --disable-optimization --ghc-options=-w
 
 script:
   - cabal configure --enable-tests --disable-optimization && cabal build