Update the Mac build script to include the conformance tests

- Kick off the conformance tests
- Add missing ignore for something generated by a build on the conformance directory.
diff --git a/.gitignore b/.gitignore
index 4648712..a9b0a88 100644
--- a/.gitignore
+++ b/.gitignore
@@ -104,4 +104,5 @@
 conformance/conformance-test-runner
 conformance/conformance.pb.cc
 conformance/conformance.pb.h
+conformance/conformance.rb
 conformance/protoc_middleman