Fix build file

Truth8 was missing, added to build file.

Change-Id: Ia71c38fe419c244486cde1166d0c00d1b64ba152

javatests/com/google/gerrit/plugins/checks/rules/BUILD

diff --git a/javatests/com/google/gerrit/plugins/checks/rules/BUILD b/javatests/com/google/gerrit/plugins/checks/rules/BUILD
index 17fdb2a..2e76709 100644
--- a/javatests/com/google/gerrit/plugins/checks/rules/BUILD
+++ b/javatests/com/google/gerrit/plugins/checks/rules/BUILD
@@ -14,6 +14,7 @@
         "//lib:guava",
         "//lib/jgit/org.eclipse.jgit:jgit",
         "//lib/truth",
+        "//lib/truth:truth-java8-extension",
         "//plugins/checks:checks__plugin",
     ],
 )