Upgrade dependencies to support future migration to Java 9.

[millems]

1. Migrated from FindBugs to SpotBugs
2. Upgraded any dependencies that no longer worked on Java 9
3. Added explicit dependency on javax annotations for @generated annotation access.
4. Fixed a warning from SpotBugs that was not caught by FindBugs.

[dagnir]

Think we also need to update to Trusty to get 9

[spfink]

What kind of testing have you done to verify this will work for all consumers?

[millems]

Talked about it, and it might be good to wait a while before upgrading to Java 9. I'd guess most testers are still on Java 8. Upgrading later on when more people have had a chance to upgrade is probably the better idea.

I'm going to tweak this PR to include everything BUT actually performing the java 9 upgrade. That'll make it a 1-character change to upgrade when we are ready.

[brharrington]

Talked about it, and it might be good to wait a while before upgrading to Java 9.

Does this mean that the 2.x SDK will require jdk9 or higher at runtime? Since jdk9 is not considered a long term stable release, it seems like it would be good if it could run on jdk8 until at least 18.9 is out.

As a side note, given you are still supporting jdk8 for now, why not configure a travis matrix build that verifies changes on both jdk8 and jdk9? We have been doing that and it has helped prevent a few regressions from coming in and breaking support for running on jdk9.