Fix TypeError in BlockQueue.push() #341 (#342)

* fix TypeError #341

* use f-string to display fork

hive/steem/block/stream.py

@@ -35,11 +35,11 @@ def push(self, block):
         next_hash = block['block_id']
         next_prev = block['previous']
         if self._prev != next_prev:
-            fork = "%s--> %s->%s" % (self._prev, next_prev, next_hash)
+            fork = f"{self._prev}--> {next_prev}->{next_hash}"
             if self._queue: # if using max_size>0, fork might be in buffer only
                 buff = self.size()
                 alert = "NOTIFYALERT " if buff < self._max_size else ""
-                raise MicroForkException("%squeue:%d %s" % (alert, fork, buff))
+                raise MicroForkException(f"{alert}queue:{buff} {fork}")
             raise ForkException("NOTIFYALERT fork " + fork)
 
         self._prev = next_hash