Bump error-prone from 2.1.2 to 2.1.3

Bump error-prone from 2.1.2 to 2.1.3

and some code changes now required by enabling a few extra checks which
in the first round I could not enable because of un-fixable violations
in Immutables.org generated code (which could possibly have affected
YANG generated code as well later)

With with the new XepExcludedPaths, see
https://github.com/google/error-prone/issues/821 (instead of
https://github.com/google/error-prone/issues/808), we can ignore
/target/ so that's not a problem, anymore.

The disabled StaticOrDefaultInterfaceMethod is because I've hit it
during the build of caches/ but learnt its very Android specific, we
don't care, see
http://errorprone.info/bugpattern/StaticOrDefaultInterfaceMethod

The added FutureReturnValueIgnored is GREAT.

Change Log on
https://groups.google.com/forum/#!msg/error-prone-announce/-ExdzeDOURY/7cQqwSezCQAJ

Change-Id: I05d5497626240d1a30cc54ee3014f1dbe367fcb5
Signed-off-by: Michael Vorburger <vorburger@redhat.com>