Update .ruby-version to match version used in CI
Exclude .git, spec, and coverage reports from package

There's no need for a packaged admin buildpack to contain all of the
test artifacts, coverage reports, or git repository so exclude them
from the zip when it's created.
Document config/licenses.yml in installation.md

* Document licenses.yml
* Add explicit git ignore for config/licenses.yml
Merge pull request #44 from sykesm/ruby-version

Update .ruby-version to match version used in CI
Merge pull request #45 from sykesm/package-excludes

Exclude .git, spec, and coverage reports from package
Merge pull request #46 from sykesm/document-config-licenses

Document config/licenses.yml in installation.md
Merge remote branch 'upstream/master'