encoding/gob: fix doc typo

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/6300078

src/pkg/encoding/gob/doc.go

@@ -116,7 +116,7 @@ uninterpreted bytes of the value.
 All other slices and arrays are sent as an unsigned count followed by that many
 elements using the standard gob encoding for their type, recursively.
 
-Maps are sent as an unsigned count followed by that man key, element
+Maps are sent as an unsigned count followed by that many key, element
 pairs. Empty but non-nil maps are sent, so if the sender has allocated
 a map, the receiver will allocate a map even no elements are
 transmitted.