Fix tag mismatch in podspec (#477)

The tags for this repo *usually* dont have a `v` prefix, so doing a `pod install` with a direct dependency on the podspec fails. This fixes that mismatch.

RNSVG.podspec

@@ -9,7 +9,7 @@ Pod::Spec.new do |s|
   s.license          = package['license']
   s.homepage         = 'https://github.com/magicismight/react-native-svg'
   s.authors          = 'Horcrux Chen'
-  s.source           = { :git => 'https://github.com/magicismight/react-native-svg.git', :tag => "v#{s.version}" }
+  s.source           = { :git => 'https://github.com/magicismight/react-native-svg.git', :tag => s.version }
   s.source_files     = 'ios/**/*.{h,m}'
   s.requires_arc     = true
   s.platforms        = { :ios => "8.0", :tvos => "9.2" }