go.tools/go/types: fix doc comment
go.tools/go/types: fix doc comment

LGTM=adonovan
R=adonovan
CC=golang-codereviews
https://golang.org/cl/90100043

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