servlet_tests: Use size=small

Bazel provides a warning for tests that can use the small size but are
using the default 'moderate'. Update the test size to remove the
warning.

Change-Id: I44a3057296d6fc1802196bed984c8f7344f57817

javatests/com/google/gitiles/BUILD

diff --git a/javatests/com/google/gitiles/BUILD b/javatests/com/google/gitiles/BUILD
index c67e565..4021114 100644
--- a/javatests/com/google/gitiles/BUILD
+++ b/javatests/com/google/gitiles/BUILD
@@ -34,6 +34,7 @@
         ],
         exclude = ["**/ServletTest.java"],
     ),
+    size = "small",
     visibility = ["//visibility:public"],
     runtime_deps = ["//lib/junit:hamcrest-core"],
     deps = DEPS + [