Added an ignore flag for .DS_Store files and fixed up some spacing.

.gitignore

@@ -1,5 +1,7 @@
-# Xcode
+# Mac OS X
+.DS_Store
 
+# Xcode
 build/
 *.pbxuser
 !default.pbxuser
@@ -18,5 +20,4 @@ DerivedData
 *.xcuserstate
 
 # Carthage
-
 Carthage/Build