restrict haddock < 2.14 due to GHC version issues

Haddock versions >= 2.14 are failing to install with GHC 7.6.*:

```
Preprocessing library haddock-2.14.2...
  src/Haddock/InterfaceFile.hs:85:2:
    error: #error Unsupported GHC version
```

and with 7.4 `src/Haddock/Parser.hs:5:14: Unsupported extension: LambdaCase`

Author: tavisrudd

scripts/install-deps.sh

@@ -2,7 +2,7 @@ $CABAL update\
   && $CABAL install alex happy cpphs -j$NUM_CPU\
   && if ! [[ $GHCVER == "head" || -n $SKIP_HADDOCK ]]
        then
-         $CABAL install haddock -j$NUM_CPU
+         $CABAL install 'haddock < 2.14' -j$NUM_CPU
      fi\
   && if ! [[ -z "$EXTRA_DEPS_PRE" ]]
        then