Add injection folder to ignore

After trying this tool for code injeciton: https://github.com/johnno1962/injectionforxcode we added it to our workflow.
Only bad side is that there's a folder included in the project that would be worth ignoring.
We had it in our .gitignore file. Just pushing the change

Author: wolffan

Objective-C.gitignore

@@ -51,3 +51,10 @@ Carthage/Build
 
 fastlane/report.xml
 fastlane/screenshots
+
+#Code Injection
+#
+# After new code Injection tools there's a generated folder /iOSInjectionProject
+# https://github.com/johnno1962/injectionforxcode
+
+iOSInjectionProject/