upgraded jwcrypto to fix the r/s bug closes #616

package.json

@@ -25,7 +25,7 @@
     , "colors" : "0.5.0"
     , "sax" : "0.2.3"
     , "mimelib-noiconv" : "0.1.3"
-    , "jwcrypto": "https://github.com/mozilla/jwcrypto/tarball/e02d4ea"
+    , "jwcrypto": "https://github.com/mozilla/jwcrypto/tarball/de57b1891"
     , "postprocess": "0.0.3"
     , "urlparse": "0.0.1"
   }