Fix asyncio.streams.FlowControlMixin docstring typo. (#4578)

diff --git a/Lib/asyncio/streams.py b/Lib/asyncio/streams.py
index 05774e9..15c9513 100644
--- a/Lib/asyncio/streams.py
+++ b/Lib/asyncio/streams.py
@@ -154,7 +154,7 @@
     """Reusable flow control logic for StreamWriter.drain().
 
     This implements the protocol methods pause_writing(),
-    resume_reading() and connection_lost().  If the subclass overrides
+    resume_writing() and connection_lost().  If the subclass overrides
     these it must call the super methods.
 
     StreamWriter.drain() must wait for _drain_helper() coroutine.