playground: add package from golang.org/x/talks
playground: add package from golang.org/x/talks

This adds the package golang.org/x/talks/2016/applicative/google so
Sameer's slide linked below will work correctly.

https://talks.golang.org/2016/applicative.slide#34

Change-Id: I14254792babfe08a57719121377eaa525e78a340
Reviewed-on: https://go-review.googlesource.com/24320
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>

golang/playground,golang/playground,golang/playground