* Remove version pin for java-diff-utils dependency
Latest version of the lib introduces a small behavior change/bug fix.
It no longer ignores empty lines. This actually makes sense.
Update the test data to reflect this change.
* Add test for Java 8 Compatibility
Add a test to check for Java 8 compatibility of jars deployed to
AppEngine.
It is not enough to run existing tests with Java 8 VM, since many API
jars are not exercised by tests. For example, those for GCP services
like the SecretManager.
We take the conservative approach and verify that every class in every
jar are compiled for Java 8.
Weimin Yu