Use shellcheck tool to test bash scripts under /scripts

See https://github.com/koalaman/shellcheck

.travis.yml

@@ -7,6 +7,7 @@ notifications:
 install:
     - brew install python
     - brew link --overwrite python
+    - brew install shellcheck
     - pip install -r requirements-dev.txt
 script:
     - nosetests ./tests/test_dtruss.py || echo "Temporary workaround for dtruss tests failing without a reason. See issue 23"
@@ -14,3 +15,4 @@ script:
     - nosetests ./tests/test_ipconnections.py
     - nosetests ./tests/test_analyzer.py
     - nosetests ./tests/test_packages.py
+    - shellcheck ./scripts/*