Enable error-prone checks by default

Based on recent work by Dave Borowitz on the Gerrit project [1, 2].

The warnings/error configuration is unchanged, but now the checks are
enabled by default during the build rather than having to be manually
invoked.

[1] https://gerrit-review.googlesource.com/c/gerrit/+/225653
[2] https://gerrit-review.googlesource.com/c/gerrit/+/225714

Change-Id: I7f4849896af72de38880b13d64519cc93bb3d2a3
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>
diff --git a/.bazelrc b/.bazelrc
index 2a990c7..3a61f8c 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -2,6 +2,7 @@
 build --experimental_strict_action_env
 build --action_env=PATH
 build --disk_cache=~/.gerritcodereview/bazel-cache/cas
+build --java_toolchain //tools:error_prone_warnings_toolchain
 
 test --build_tests_only
 test --test_output=errors