Added swift_version into podspec

Kenneth Tsang · Kenneth Tsang · commit 7632fb0eb55a · 2018-10-03T16:32:14.000+08:00
diff --git a/NumberField.podspec b/NumberField.podspec
@@ -29,6 +29,7 @@ Numeric field with Numpad keyboard on both iPhone and iPad.
   # s.social_media_url = 'https://twitter.com/<TWITTER_USERNAME>'
 
   s.ios.deployment_target = '9.0'
+  s.swift_version = '4.2'
 
   s.source_files = 'NumberField/Classes/**/*'
   
