Don't build benchmarks on travis-ci

Trying to install the benchmark dependencies causes a dependency
cycle.

Author: tibbe

.travis.yml

@@ -14,13 +14,15 @@ before_install:
  - sudo apt-get install cabal-install-1.18 ghc-$GHCVER happy
  - export PATH=/opt/ghc/$GHCVER/bin:$PATH
 
+# Benchmarks aren't built as installing their dependencies causes a
+# dependency cycle.
 install:
  - cabal-1.18 update
- - cabal-1.18 install --only-dependencies --enable-tests --enable-benchmarks
+ - cabal-1.18 install --only-dependencies --enable-tests
 
 # Here starts the actual work to be performed for the package under test; any command which exits with a non-zero exit code causes the build to fail.
 script:
- - cabal-1.18 configure --enable-tests --enable-benchmarks -v2  # -v2 provides useful information for debugging
+ - cabal-1.18 configure --enable-tests -v2  # -v2 provides useful information for debugging
  - cabal-1.18 build   # this builds all libraries and executables (including tests/benchmarks)
  - cabal-1.18 test
  - cabal-1.18 check