cmd/godoc: add golang.org/x/playground custom import path
cmd/godoc: add golang.org/x/playground custom import path

Change-Id: Ic399dbf8a77e7c61ba8be263515b13a6b488b4e9
Reviewed-on: https://go-review.googlesource.com/2309
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

sshetty10/tools,argandas/tools,jdhenke/tools,4ad/tools,dmitris/tools,nicot/tools,nicot/tools,4ad/tools,nicot/tools,cmars/tools,glasser/golang-tools,cw2018/tools,sshetty10/tools,springning/tools,matryer/tools,golang/tools,golang/tools,josharian/tools,maddyonline/tools,golang/tools,glasser/golang-tools,runcom/tools,maddyonline/tools,cw2018/tools,jdhenke/tools,josharian/tools,golang/tools,magiccao/tools,dmitris/tools,matryer/tools,josharian/tools,glasser/golang-tools,jdhenke/tools,cmars/tools,josharian/tools,nicot/tools,syreclabs/go-tools,cmars/tools,syreclabs/go-tools,springning/tools,cw2018/tools,matryer/tools,cw2018/tools,maddyonline/tools,syreclabs/go-tools,springning/tools,matryer/tools,golang/tools,magiccao/tools,glasser/golang-tools,sshetty10/tools,sshetty10/tools,4ad/tools,argandas/tools,syreclabs/go-tools,cmars/tools,springning/tools,dmitris/tools,maddyonline/tools,runcom/tools,syreclabs/go-tools,argandas/tools,magiccao/tools,magiccao/tools,syreclabs/go-tools,argandas/tools,jdhenke/tools,dmitris/tools,runcom/tools,runcom/tools