[3.7] Fix duplicating words words. (GH-6296) (GH-6297)

Most of them have been added in 3.7.
(cherry picked from commit bac2d5ba30339298db7d4caa9c8cd31d807cf081)
diff --git a/Lib/asyncio/protocols.py b/Lib/asyncio/protocols.py
index 8904478..dc298a8 100644
--- a/Lib/asyncio/protocols.py
+++ b/Lib/asyncio/protocols.py
@@ -105,7 +105,7 @@
 class BufferedProtocol(BaseProtocol):
     """Interface for stream protocol with manual buffer control.
 
-    Important: this has been been added to asyncio in Python 3.7
+    Important: this has been added to asyncio in Python 3.7
     *on a provisional basis*!  Consider it as an experimental API that
     might be changed or removed in Python 3.8.