imports: fix LocalPrefix document prefix
imports: fix LocalPrefix document prefix

golint suggested:
  comment on exported var LocalPrefix should be of the form "LocalPrefix ..."

Change-Id: I1d2f92ba76e3c091440f676936dbb1fc1ce07f3a
Reviewed-on: https://go-review.googlesource.com/46432
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

syreclabs/go-tools,syreclabs/go-tools,golang/tools,syreclabs/go-tools,syreclabs/go-tools,golang/tools,golang/tools,syreclabs/go-tools,golang/tools,syreclabs/go-tools,golang/tools