Reverting change to ignore build subdirectories

Reverted a change that was causing build directories at the root folder to show up in git.  If you need to ignore subdirectories the leading slash needs to be omitted.

Objective-C.gitignore

 # Xcode
 .DS_Store
-*/build/*
+build/
 *.pbxuser
 !default.pbxuser
 *.mode1v3