Re-enable cabal check on Travis

Author: ivan-m

.travis.yml

@@ -89,6 +89,7 @@ script:
  - cabal configure --enable-tests --enable-benchmarks -v2  # -v2 provides useful information for debugging
  - cabal build   # this builds all libraries and executables (including tests/benchmarks)
  - cabal test
+ - cabal check
  - cabal sdist   # tests that a source-distribution can be generated
 
 # Check that the resulting source distribution can be built & installed.