windows: correct misspelling in comment

The comment for ConsoleScreenBufferInfo uses the word 'retreive' that
is a misspelling of 'retrieve'.

Change-Id: Idd9fb0c5082b6a2b10badbbb162e312710bfe68b
GitHub-Last-Rev: 08d62a57df113291ea0abd7198bae7d15fa6f075
GitHub-Pull-Request: golang/sys#18
Reviewed-on: https://go-review.googlesource.com/134221Reviewed-by: Ian Lance Taylor <iant@golang.org>

windows/types_windows.go

@@ -1453,7 +1453,7 @@ type SmallRect struct {
 	Bottom int16
 }
 
-// Used with GetConsoleScreenBuffer to retreive information about a console
+// Used with GetConsoleScreenBuffer to retrieve information about a console
 // screen buffer. See
 // https://docs.microsoft.com/en-us/windows/console/console-screen-buffer-info-str
 // for details.