Change oyoyo tokenbucket to be consistent with !wait TB

In !wait, the delay is how long it takes (in seconds) to add one token,
whereas in oyoyo the delay was the opposite (lower = longer refill).

IMO the !wait one makes more sense, so change oyoyo to match.

oyoyo/client.py

@@ -58,7 +58,7 @@ class TokenBucket(object):
     def tokens(self):
         now = time.time()
         if self._tokens < self.capacity:
-            delta = self.fill_rate * (now - self.timestamp)
+            delta = (now - self.timestamp) / self.fill_rate
             self._tokens = min(self.capacity, self._tokens + delta)
         self.timestamp = now
         return self._tokens