Bazel: Increase severity of ClassCanBeStatic to ERROR

Change-Id: I8250fd15cfff6bbba54a238be31b3cf772edab3f
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

tools/BUILD

@@ -29,7 +29,7 @@ java_package_configuration(
         "-Xep:BadComparable:WARN",
         "-Xep:BoxedPrimitiveConstructor:ERROR",
         "-Xep:CannotMockFinalClass:WARN",
-        "-Xep:ClassCanBeStatic:WARN",
+        "-Xep:ClassCanBeStatic:ERROR",
         "-Xep:ClassNewInstance:WARN",
         "-Xep:DefaultCharset:ERROR",
         "-Xep:DoubleCheckedLocking:WARN",