Updated podspec version to 3.7.0

SDWebImage.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name = 'SDWebImage'
-  s.version = '3.6'
+  s.version = '3.7.0'
   s.platform = :ios, '5.0'
   s.license = 'MIT'
   s.summary = 'Asynchronous image downloader with cache support with an UIImageView category.'