spec: Fix link to fallthrough statements

R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/1303041

doc/go_spec.html

@@ -3771,7 +3771,7 @@ ExprSwitchCase = "case" ExpressionList | "default" .
 <p>
 In a case or default clause,
 the last statement only may be a "fallthrough" statement
-(§<a href="#Fallthrough_statement">Fallthrough statement</a>) to
+(§<a href="#Fallthrough_statements">Fallthrough statement</a>) to
 indicate that control should flow from the end of this clause to
 the first statement of the next clause.
 Otherwise control flows to the end of the "switch" statement.