Linux: Add .build/ to gitignore

.gitignore

@@ -23,4 +23,6 @@ DerivedData
 # you should judge for yourself, the pros and cons are mentioned at:
 # http://guides.cocoapods.org/using/using-cocoapods.html#should-i-ignore-the-pods-directory-in-source-control
 #
-# Pods/
+# Pods/
+
+.build/