Use cabal-install-1.20. Allow failures in head.

Author: svenpanne

.travis.yml

@@ -6,24 +6,28 @@ env:
  - GHCVER=7.8.3
  - GHCVER=head
 
+matrix:
+ allow_failures:
+  - env: GHCVER=head
+
 before_install:
  - sudo add-apt-repository -y ppa:hvr/ghc
  - sudo apt-get update -qq
- - sudo apt-get install -qq cabal-install-1.18 ghc-$GHCVER
+ - sudo apt-get install -qq cabal-install-1.20 ghc-$GHCVER
  - export PATH="/opt/ghc/$GHCVER/bin:$PATH"
 
 install:
- - cabal-1.18 update
+ - cabal-1.20 update
  - ghc --version
  - ghc-pkg list
  - pushd ..
  - git clone --depth=100 --quiet https://github.com/haskell-opengl/OpenGLRaw.git
  - cd OpenGLRaw
- - cabal-1.18 install --enable-documentation
+ - cabal-1.20 install --enable-documentation
  - popd
  - ghc-pkg list
 
 script:
- - cabal-1.18 install --enable-documentation
- - cabal-1.18 sdist --verbose=3
+ - cabal-1.20 install --enable-documentation
+ - cabal-1.20 sdist
  - ghc-pkg list