Bump pod version to 0.5.1

SocketRocket.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name               = "SocketRocket"
-  s.version            = '0.5.0'
+  s.version            = '0.5.1'
   s.summary            = 'A conforming WebSocket (RFC 6455) client library.'
   s.homepage           = 'https://github.com/square/SocketRocket'
   s.authors            = 'Square'