Add hpack to travis script

.travis.yml

@@ -50,8 +50,12 @@ before_install:
   - "PATH=/opt/ghc/bin:/opt/ghc-ppa-tools/bin:$HOME/local/bin:$PATH"
   - HCNUMVER=$(( $(${HC} --numeric-version|sed -E 's/([0-9]+)\.([0-9]+)\.([0-9]+).*/\1 * 10000 + \2 * 100 + \3/') ))
   - echo $HCNUMVER
+  - curl -L https://github.com/sol/hpack/releases/download/0.28.2/hpack_linux.gz --output $HOME/.local/bin/hpack.gz
+  - gunzip $HOME/.local/bin/hpack.gz
+  - chmod a+x $HOME/.local/bin/hpack
 
 install:
+  - hpack
   - cabal --version
   - echo "$(${HC} --version) [$(${HC} --print-project-git-commit-id 2> /dev/null || echo '?')]"
   - BENCH=${BENCH---enable-benchmarks}
@@ -77,6 +81,7 @@ install:
 # 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:
+  - hpack
   # test that source-distributions can be generated
   - (cd "." && cabal sdist)
   - mv "."/dist/hw-excess-*.tar.gz ${DISTDIR}/