blog: fix Yacc links in the generating code post

The post has a dead link to the Go version of Yacc (goyacc).
It was moved to 'golang.org/x/tools/cmd/goyacc' in CL 27325.

Fixes golang/go#20434.

Change-Id: I16e39d0bc2be422b129fd5cadd95f9b3a52c1abd
Reviewed-on: https://go-review.googlesource.com/44230
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed