Bazel: Increase severity of MissingFail to ERROR

All instances of this potential bug have been cleaned up in
preceding commits. Increase the severity to ERROR so that it
is easier to detect reoccurences.

Change-Id: I25beebcea1f01f468e0f2b1d24a83511029c077c
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

tools/BUILD

@@ -53,7 +53,7 @@ java_package_configuration(
         "-Xep:JUnit3FloatingPointComparisonWithoutDelta:WARN",
         "-Xep:JUnitAmbiguousTestClass:WARN",
         "-Xep:LiteralClassName:WARN",
-        "-Xep:MissingFail:WARN",
+        "-Xep:MissingFail:ERROR",
         "-Xep:MissingOverride:WARN",
         "-Xep:MutableConstantField:WARN",
         "-Xep:NarrowingCompoundAssignment:WARN",