modernize python3 syntax

src/sakia/data/entities/connection.py

@@ -24,10 +24,10 @@ class Connection:
     password = attr.ib(init=False, converter=str, default="", cmp=False, hash=False)
 
     def is_identity(self):
-        return self.uid is not ""
+        return self.uid != ""
 
     def is_wallet(self):
-        return self.uid is ""
+        return self.uid == ""
 
     def title(self):
         return "@".join([self.uid, self.pubkey[:11]])