wadors (loadimage) must return a deferred like wadouri does (PR #64)

If a promise is returned instead of a deferred, imageCache
(purgeCacheIfNecessary) will break because it calls reject()
on every item removed from the cache.

Pull request
https://github.com/chafey/cornerstoneWADOImageLoader/pull/64

Packages/ohif-cornerstone/client/cornerstoneWADOImageLoader.js

@@ -4352,7 +4352,7 @@ var JpegImage = (function jpegImage() {
       deferred.reject(reason);
     });
 
-    return deferred.promise();
+    return deferred;
   }
 
   // registery dicomweb and wadouri image loader prefixes