fix: podspec file to match the expections of Cocoapods.

In 5e6cec3 this file got added, and at
that time we missed renaming/modifying it.

A Podspec file, or Spec, describes a version of a Pod library.
It includes details about where the source files are located,
which files to use, the build settings to apply, dependencies,
frameworks used and other general metadata such as the name,
version and description for the Pod.

Author: jordanyaker

react-native-cameraroll.podspec react-native-picker.podspecreact-native-cameraroll.podspec renamed to react-native-picker.podspec

@@ -12,7 +12,7 @@ Pod::Spec.new do |s|
   s.homepage     = package['homepage']
   s.platform     = :ios, "9.0"
 
-  s.source       = { :git => "https://github.com/react-native-community/react-native-picker.git", :tag => "#{s.version}" }
+  s.source       = { :git => "https://github.com/react-native-community/react-native-picker.git", :tag => "v#{s.version}" }
   s.source_files  = "ios/**/*.{h,m}"
 
   s.dependency 'React'