Add CONTRIBUTING.rst to MANIFEST.in

Also, intentionally exclude TravisCI files, to match excluding test
files, and make check-manifest happy.

Author: jwhitlock

MANIFEST.in

@@ -1,10 +1,11 @@
 recursive-include pipeline/templates *.html *.jinja
 recursive-include pipeline/jinja2 *.html *.jinja
-include AUTHORS LICENSE README.rst HISTORY.rst
+include AUTHORS LICENSE README.rst HISTORY.rst CONTRIBUTING.rst
 recursive-include tests *
 recursive-exclude tests *.pyc *.pyo
 recursive-exclude tests/node_modules *
 recursive-exclude tests/npm-cache *
 recursive-exclude tests/npm *
 include docs/Makefile docs/make.bat docs/conf.py
 recursive-include docs *.rst
+exclude package.json requirements.txt tox.ini