go/importer: fix doc typo

Fix the following issue detected by golint:

	import.go:9:1: package comment should be of the form "Package importer ..."

It makes the package comment more consistent with other packages.

Change-Id: I1415066c136ce249af19d70848a38203caf7c9c7
Reviewed-on: https://go-review.googlesource.com/21177
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed