Fix grammar in asyncio-dev.rst (GH-15672)
Automerge-Triggered-By: @ned-deily
diff --git a/Doc/library/asyncio-dev.rst b/Doc/library/asyncio-dev.rst
index b728803..101e781 100644
--- a/Doc/library/asyncio-dev.rst
+++ b/Doc/library/asyncio-dev.rst
@@ -119,7 +119,7 @@
by 1 second.
An executor can be used to run a task in a different thread or even in
-a different process to avoid blocking block the OS thread with the
+a different process to avoid blocking the OS thread with the
event loop. See the :meth:`loop.run_in_executor` method for more
details.