Use a weak reference for the delegate.

Fix #78.

SocketRocket/SRWebSocket.h

@@ -50,7 +50,7 @@ extern NSString *const SRHTTPResponseErrorKey;
 
 @interface SRWebSocket : NSObject <NSStreamDelegate>
 
-@property (nonatomic, assign) id <SRWebSocketDelegate> delegate;
+@property (nonatomic, weak) id <SRWebSocketDelegate> delegate;
 
 @property (nonatomic, readonly) SRReadyState readyState;
 @property (nonatomic, readonly, retain) NSURL *url;