fmt: fix typo

Fixes #17955

Change-Id: Ia1a04796353c83358a38a6b63f2a0cd3c6926f09
Reviewed-on: https://go-review.googlesource.com/33338
Reviewed-by: Rob Pike <r@golang.org>

src/fmt/format.go

@@ -46,7 +46,7 @@ type fmt struct {
 	wid  int // width
 	prec int // precision
 
-	// intbuf is large enought to store %b of an int64 with a sign and
+	// intbuf is large enough to store %b of an int64 with a sign and
 	// avoids padding at the end of the struct on 32 bit architectures.
 	intbuf [68]byte
 }