Bazel: Increase severity of ExpectedExceptionChecker to ERROR

Incorrect usage of ExpectedException has been cleaned up in the
preceding commits. Increase the severity from WARN to ERROR so
that it is easier to catch any reoccurences.

Change-Id: I57decf620b37e85413bda53723f839c02b488f2c
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

tools/BUILD

@@ -36,7 +36,7 @@ java_package_configuration(
         "-Xep:ElementsCountedInLoop:WARN",
         "-Xep:EqualsHashCode:WARN",
         "-Xep:EqualsIncompatibleType:WARN",
-        "-Xep:ExpectedExceptionChecker:WARN",
+        "-Xep:ExpectedExceptionChecker:ERROR",
         "-Xep:Finally:WARN",
         "-Xep:FloatingPointLiteralPrecision:WARN",
         "-Xep:FragmentInjection:WARN",