Add the missing license information

iRate/1.3.2/iRate.podspec

@@ -1,6 +1,7 @@
 Pod::Spec.new do |s|
   s.name     = 'iRate'
   s.version  = '1.3.2'
+  s.license  = 'zlib'
   s.summary  = 'A handy class that prompts users of your iPhone or Mac App Store app to rate your application after using it for a while. Similar to Appirater, but with a simpler, cleaner interface and automatic support for iOS fast application switching.'
   s.homepage = 'http://charcoaldesign.co.uk/source/cocoa#irate'
   s.author   = 'Nick Lockwood'