Update Cloud9.gitignore

The next version of Cloud9 will use a top-level .c9 folder in the workspace for settings and metadata.
Ignore the build result of ATL Project.

This commit Makes VisualStudio.gitignore ignore the three items below. It needs when you create an ATL Project.

* [Dd]ebugPS/
* [Rr]eleasePS/
* dlldata.c