Bazel: Add fixes for --incompatible_load_java_rules_from_bzl

Change-Id: I5c37e69dd371c3e24a7981f632bd3e58741679d3

lib/truth/BUILD

diff --git a/lib/truth/BUILD b/lib/truth/BUILD
index 22b79cf..5a57e6d 100644
--- a/lib/truth/BUILD
+++ b/lib/truth/BUILD
@@ -1,3 +1,5 @@
+load("@rules_java//java:defs.bzl", "java_library")
+
 java_library(
     name = "truth",
     visibility = ["//visibility:public"],