devapp: update source code link
devapp: update source code link

The homepage linked only to the older godash package, when in reality
dev.golang.org is being served by the devapp package.

Adds a <title> to the page and adds closing </body> and </html> tags.

Change-Id: I71ee1e8739094c4cc8489d9759e5b3aabf610771
Reviewed-on: https://go-review.googlesource.com/34927
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/build,golang/build,golang/build,golang/build