runtime: fix minor doc typo

Change-Id: I0a1ebaf41a1bc95508fd9aa782953ddca5ef49c9
Reviewed-on: https://go-review.googlesource.com/c/go/+/169724
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/runtime/map.go

@@ -288,7 +288,7 @@ func makemap64(t *maptype, hint int64, h *hmap) *hmap {
 	return makemap(t, int(hint), h)
 }
 
-// makehmap_small implements Go map creation for make(map[k]v) and
+// makemap_small implements Go map creation for make(map[k]v) and
 // make(map[k]v, hint) when hint is known to be at most bucketCnt
 // at compile time and the map needs to be allocated on the heap.
 func makemap_small() *hmap {