go spec: fix local link

Fixes #1543.

R=rsc, r2
CC=golang-dev
https://golang.org/cl/4169068

doc/go_spec.html

 <!-- title The Go Programming Language Specification -->
-<!-- subtitle Version of February 19, 2011 -->
+<!-- subtitle Version of February 22, 2011 -->
 
 <!--
 TODO
@@ -4796,7 +4796,7 @@ The PackageName is used in <a href="#Qualified_identifiers">qualified identifier
 to access the exported identifiers of the package within the importing source file.
 It is declared in the <a href="#Blocks">file block</a>.
 If the PackageName is omitted, it defaults to the identifier specified in the
-<a href="#Package_clauses">package clause</a> of the imported package.
+<a href="#Package_clause">package clause</a> of the imported package.
 If an explicit period (<code>.</code>) appears instead of a name, all the
 package's exported identifiers will be declared in the current file's
 file block and can be accessed without a qualifier.