Update Erlang.gitignore

/ebin can't be simply ignored because *.app should be put here.

[Erlang Applications](http://erlang.org/doc/design_principles/applications.html)
> 8.4  Directory Structure
> ebin - Contains the Erlang object code, the beam files. The .app file is also placed here.

Erlang.gitignore

@@ -4,7 +4,7 @@ deps
 *.beam
 *.plt
 erl_crash.dump
-ebin
+ebin/*.beam
 rel/example_project
 .concrete/DEV_MODE
 .rebar