ios: change podspec s.dependency'

from 'React/Core  to 'React-Core fix #41

Author: zxcpoiu

RNVoipPushNotification.podspec

@@ -14,5 +14,5 @@ Pod::Spec.new do |s|
   s.requires_arc        = true
   s.platform            = :ios, "8.0"
   s.source_files        = "ios/RNVoipPushNotification/*.{h,m}"
-  s.dependency 'React/Core'
+  s.dependency 'React-Core'
 end