See if cabal-install improvements speed up enough to ditch timeouts

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

.travis.yml

@@ -57,22 +57,15 @@ matrix:
    # We axed GHC 7.6 and earlier because it's not worth the trouble to
    # make older GHC work with clang's cpp.  See
    # https://ghc.haskell.org/trac/ghc/ticket/8493
-   - env: GHCVER=7.8.4 SCRIPT=script CABAL_LIB_ONLY=YES
+   - env: GHCVER=7.8.4 SCRIPT=script
      os: osx
      osx_image: xcode6.4 # We need 10.10
-   - env: GHCVER=7.8.4 SCRIPT=script CABAL_INSTALL_ONLY=YES
-     os: osx
-     osx_image: xcode6.4
 
    # TODO: We might want to specify OSX version
    # https://docs.travis-ci.com/user/osx-ci-environment/#OS-X-Version
-   - env: GHCVER=7.10.3 SCRIPT=script CABAL_LIB_ONLY=YES
-     os: osx
-   - env: GHCVER=7.10.3 SCRIPT=script CABAL_INSTALL_ONLY=YES
-     os: osx
-   - env: GHCVER=8.0.1 SCRIPT=script CABAL_LIB_ONLY=YES
+   - env: GHCVER=7.10.3 SCRIPT=script
      os: osx
-   - env: GHCVER=8.0.1 SCRIPT=script CABAL_INSTALL_ONLY=YES
+   - env: GHCVER=8.0.1 SCRIPT=script
      os: osx
    - env: GHCVER=8.0.1 SCRIPT=bootstrap
      os: osx