Set indent to 4 spaces for BUCK*
Set indent to 4 spaces for BUCK*

Summary:
Idea (as well as [a dozen other editors](https://editorconfig.org/#download)) understand `.editorconfig` out of the box.

`BUCK*` files in `buck` repository are idented with 4 spaces.

Reviewed By: mykola-semko

shipit-source-id: 21572cd34f

Addepar/buck,kageiit/buck,nguyentruongtho/buck,facebook/buck,JoelMarcey/buck,Addepar/buck,Addepar/buck,kageiit/buck,JoelMarcey/buck,nguyentruongtho/buck,Addepar/buck,kageiit/buck,kageiit/buck,JoelMarcey/buck,zpao/buck,nguyentruongtho/buck,Addepar/buck,Addepar/buck,facebook/buck,zpao/buck,JoelMarcey/buck,facebook/buck,JoelMarcey/buck,nguyentruongtho/buck,Addepar/buck,Addepar/buck,zpao/buck,zpao/buck,facebook/buck,JoelMarcey/buck,nguyentruongtho/buck,Addepar/buck,Addepar/buck,kageiit/buck,JoelMarcey/buck,zpao/buck,JoelMarcey/buck,JoelMarcey/buck,Addepar/buck,kageiit/buck,zpao/buck,facebook/buck,JoelMarcey/buck,nguyentruongtho/buck,zpao/buck,JoelMarcey/buck,kageiit/buck,nguyentruongtho/buck,JoelMarcey/buck,Addepar/buck,facebook/buck,facebook/buck,Addepar/buck,JoelMarcey/buck