Fix small exception typos in Lib (#818)

diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 8f93976..5dfc1f0 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -766,7 +766,7 @@
 
     def flush(self):
         if self.closed:
-            raise ValueError("flush of closed file")
+            raise ValueError("flush on closed file")
         self.raw.flush()
 
     def close(self):
@@ -1214,7 +1214,7 @@
 
     def _flush_unlocked(self):
         if self.closed:
-            raise ValueError("flush of closed file")
+            raise ValueError("flush on closed file")
         while self._write_buf:
             try:
                 n = self.raw.write(self._write_buf)
diff --git a/Lib/asyncio/windows_utils.py b/Lib/asyncio/windows_utils.py
index 7c63fb9..d65ea17 100644
--- a/Lib/asyncio/windows_utils.py
+++ b/Lib/asyncio/windows_utils.py
@@ -149,7 +149,7 @@
 
     def fileno(self):
         if self._handle is None:
-            raise ValueError("I/O operatioon on closed pipe")
+            raise ValueError("I/O operation on closed pipe")
         return self._handle
 
     def close(self, *, CloseHandle=_winapi.CloseHandle):