[x/blog] blog: fix link to cgo source file in Cgo post.
[x/blog] blog: fix link to cgo source file in Cgo post.

Change-Id: Id22ff1842f85ceb312c2f5e37e6440e7e80ac727
Reviewed-on: https://go-review.googlesource.com/15690
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>
X-Blog-Commit: 79041e95580188957ec65fdbbf4b3a8b81f95fda

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website