update BUILD files

vendor/github.com/docker/engine-api/client/BUILD

@@ -70,6 +70,7 @@ go_library(
         ],
         "//conditions:default": [],
     }),
+    importpath = "github.com/docker/engine-api/client",
     visibility = ["//visibility:public"],
     deps = [
         "//vendor/github.com/docker/distribution/reference:go_default_library",

vendor/github.com/docker/engine-api/client/transport/BUILD

@@ -6,6 +6,7 @@ go_library(
         "client.go",
         "transport.go",
     ],
+    importpath = "github.com/docker/engine-api/client/transport",
     visibility = ["//visibility:public"],
     deps = ["//vendor/github.com/docker/go-connections/sockets:go_default_library"],
 )

vendor/github.com/docker/engine-api/client/transport/cancellable/BUILD

@@ -7,6 +7,7 @@ go_library(
         "canceler_go14.go",
         "cancellable.go",
     ],
+    importpath = "github.com/docker/engine-api/client/transport/cancellable",
     visibility = ["//visibility:public"],
     deps = [
         "//vendor/github.com/docker/engine-api/client/transport:go_default_library",