Add some mojom.stamp files to public/.gitignore.

This makes it match the copy in the fuchsia mojo repo.

Review URL: .

Cr-Mirrored-Commit: d3823ef2b8141c42724a35c69257b0232e133462
diff --git a/.gitignore b/.gitignore
index 031ef3a..f99f2ab 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,7 +3,9 @@
 # Download the Mojom parser binary.
 # Download the mojom generators.
 # A generator is anything in the generators directory except sha1 files.