add oUnit file to .gitignore

Reviewed By: cristianoc

Differential Revision: D3047272

fb-gh-sync-id: bc38dd8
shipit-source-id: bc38dd8

.gitignore

@@ -16,6 +16,9 @@
 # Directories generated by Ocamlbuild
 _build
 
+# generated by oUnit
+/oUnit-all.cache
+
 # autoconf-generated stuff
 /acinclude.m4
 /aclocal.m4