fix(npmignore): ignore more unnecessary files (#393)

According to [cost-of-modules](https://github.com/siddharthkp/cost-of-modules)
commitizen is responsible for `76.32M` of my disk space. Most of that is
probably from dependencies, but while looking into this, I noticed that
there are several files we should probably not be publishing.

.npmignore

@@ -1,4 +1,9 @@
 /meta
 /src
 /test
-test/tools/trigger-appveyor-tests.sh
+test/tools/trigger-appveyor-tests.sh
+/coverage
+/.travis.yml
+/appveyor.yml
+jsconfig.json
+travis_after_all.py