update BUILD files

vendor/github.com/spf13/afero/BUILD

@@ -25,6 +25,7 @@ go_library(
         ],
         "//conditions:default": [],
     }),
+    importpath = "github.com/spf13/afero",
     visibility = ["//visibility:public"],
     deps = [
         "//vendor/github.com/pkg/sftp:go_default_library",

vendor/github.com/spf13/afero/mem/BUILD

@@ -7,6 +7,7 @@ go_library(
         "dirmap.go",
         "file.go",
     ],
+    importpath = "github.com/spf13/afero/mem",
     visibility = ["//visibility:public"],
 )
 

vendor/github.com/spf13/afero/sftp/BUILD

@@ -3,6 +3,7 @@ load("@io_bazel_rules_go//go:def.bzl", "go_library")
 go_library(
     name = "go_default_library",
     srcs = ["file.go"],
+    importpath = "github.com/spf13/afero/sftp",
     visibility = ["//visibility:public"],
     deps = ["//vendor/github.com/pkg/sftp:go_default_library"],
 )