Fix typo. MUL_ASSIGN is "*=", not "+=".

R=gri
APPROVED=gri
DELTA=1  (0 added, 0 deleted, 1 changed)
OCL=31879
CL=31886

src/pkg/go/token/token.go

@@ -154,7 +154,7 @@ var tokens = map [Token] string {
 
 	ADD_ASSIGN : "+=",
 	SUB_ASSIGN : "-=",
-	MUL_ASSIGN : "+=",
+	MUL_ASSIGN : "*=",
 	QUO_ASSIGN : "/=",
 	REM_ASSIGN : "%=",