Update DateTools.podspec

Author: MatthewYork

DateTools.podspec

@@ -10,7 +10,7 @@ Pod::Spec.new do |s|
   s.author       = { "Matthew York" => "my3681@gmail.com" }
 
   s.source       = { :git => "https://github.com/MatthewYork/DateTools.git",
-                     :tag => s.version.to_s }
+                     :tag => "v#{s.version.to_s}" }
 
   s.ios.platform = :ios, '7.0'
   s.osx.platform = :iox, '10.7'