fix speling

Author: jschlyter

src/cryptojwt/jws/jws.py

@@ -177,7 +177,7 @@ def verify_compact_verbose(self, jws=None, keys=None, allow_none=False,
 
             self.jwt = jwt
         elif not self.jwt:
-            raise ValueError('Missing singed JWT')
+            raise ValueError('Missing signed JWT')
         else:
             jwt = self.jwt