time: Fix typo in Time.String() description.

Refs #12914.

Change-Id: Iadac4cbef70db6a95b47f86eaffcfc63bfdb8e90
Reviewed-on: https://go-review.googlesource.com/36334
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/time/format.go

@@ -424,9 +424,9 @@ func formatNano(b []byte, nanosec uint, n int, trim bool) []byte {
 
 // String returns the time formatted using the format string
 //	"2006-01-02 15:04:05.999999999 -0700 MST"
-// 
+//
 // If the time has a monotonic clock reading, the returned string
-// includes a final field "m±<value>", where value is the monotonic
+// includes a final field "m=±<value>", where value is the monotonic
 // clock reading formatted as a decimal number of seconds.
 func (t Time) String() string {
 	s := t.Format("2006-01-02 15:04:05.999999999 -0700 MST")