Add an explicit RUBYLIB path to fix a load error under JRuby
diff --git a/ruby/compatibility_tests/v3.0.0/test.sh b/ruby/compatibility_tests/v3.0.0/test.sh
index d5a8fd7..1a9b798 100755
--- a/ruby/compatibility_tests/v3.0.0/test.sh
+++ b/ruby/compatibility_tests/v3.0.0/test.sh
@@ -14,4 +14,4 @@
 chmod +x protoc
 
 # Run tests
-rake test
+RUBYLIB=../../lib:. rake test