exclude d2go&project lib from .gitignore

Summary: It's possible to have `lib` under core `mobile-vision/d2go/{d2go,projects}`, exclude them from `.gitignore`.

Reviewed By: zhanghang1989

Differential Revision: D34288538

fbshipit-source-id: 7094cdf4f52263fbf6ff6707d487bc3328fbbd8b

.gitignore

@@ -15,6 +15,9 @@ downloads/
 eggs/
 .eggs/
 lib/
+!d2go/*/lib/
+!projects/*/lib/
+!projects_oss/*/lib/
 lib64/
 parts/
 sdist/