update BUILD files

vendor/github.com/stretchr/testify/assert/BUILD

@@ -11,6 +11,7 @@ go_library(
         "forward_assertions.go",
         "http_assertions.go",
     ],
+    importpath = "github.com/stretchr/testify/assert",
     visibility = ["//visibility:public"],
     deps = [
         "//vendor/github.com/davecgh/go-spew/spew:go_default_library",

vendor/github.com/stretchr/testify/mock/BUILD

@@ -6,6 +6,7 @@ go_library(
         "doc.go",
         "mock.go",
     ],
+    importpath = "github.com/stretchr/testify/mock",
     visibility = ["//visibility:public"],
     deps = [
         "//vendor/github.com/davecgh/go-spew/spew:go_default_library",

vendor/github.com/stretchr/testify/require/BUILD

@@ -9,6 +9,7 @@ go_library(
         "require_forward.go",
         "requirements.go",
     ],
+    importpath = "github.com/stretchr/testify/require",
     visibility = ["//visibility:public"],
     deps = ["//vendor/github.com/stretchr/testify/assert:go_default_library"],
 )