asyncio: Fix spelling and typos.

Thanks to Vajrasky Kok for discovering some of them.
diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index b7ee758..a3e7cdf 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -181,7 +181,7 @@
 
         The frames are always ordered from oldest to newest.
 
-        The optional limit gives the maximum nummber of frames to
+        The optional limit gives the maximum number of frames to
         return; by default all available frames are returned.  Its
         meaning differs depending on whether a stack or a traceback is
         returned: the newest frames of a stack are returned, but the