Clarify Groovy file search

Previously, the Spring Boot CLI documentation and the Groovy
documentation differed in how the described detection of Groovy files.
The Spring Boot CLI documentation was factually incorrect.  This
change removes mention of the root directory in the Spring Boot CLI
documentation.

[#63606768]
Merge 63606768-deep-inspection to master

[Completes #63606768]
Add Grails documentation

Previously there was no mention of Grails applications anywhere in the
documentation.  This was because Grails applications are treated as
Servlet applications and therefore didn't require anything extra.
Grails users were confused so it needed to be improved.  This change
adds Grails to the first bit of body text in the README and adds an
example of how to run Grails applications.

[#63612598]
Merge 63612598-grails-in-docs to master

[Completes #63612598]
Example Documentation

Previously, all the documentation for the Java Buildpack was reference
documentation.  This change adds the beginnings of more by adding
examples of building and deploying the artifact types that we
currently support.

[#63612640]
Merge 63612640-examples to master

[Completes #63612640]
Dependency updates

This change updates dependencies to their latest versions.
Rubocop Updates

A recent upgrade to Rubocop caused a number of new failures.  This
change fixes those failures.
Merge branch 'master' of github.com:cloudfoundry/java-buildpack

Conflicts:
	java-buildpack.iml