update BUILD files

vendor/github.com/google/certificate-transparency/go/BUILD

@@ -7,6 +7,7 @@ go_library(
         "signatures.go",
         "types.go",
     ],
+    importpath = "github.com/google/certificate-transparency/go",
     visibility = ["//visibility:public"],
     deps = ["//vendor/github.com/google/certificate-transparency/go/x509:go_default_library"],
 )

vendor/github.com/google/certificate-transparency/go/asn1/BUILD

@@ -7,6 +7,7 @@ go_library(
         "common.go",
         "marshal.go",
     ],
+    importpath = "github.com/google/certificate-transparency/go/asn1",
     visibility = ["//visibility:public"],
 )
 

vendor/github.com/google/certificate-transparency/go/client/BUILD

@@ -3,6 +3,7 @@ load("@io_bazel_rules_go//go:def.bzl", "go_library")
 go_library(
     name = "go_default_library",
     srcs = ["logclient.go"],
+    importpath = "github.com/google/certificate-transparency/go/client",
     visibility = ["//visibility:public"],
     deps = [
         "//vendor/github.com/google/certificate-transparency/go:go_default_library",

vendor/github.com/google/certificate-transparency/go/x509/BUILD

@@ -36,6 +36,7 @@ go_library(
         ],
         "//conditions:default": [],
     }),
+    importpath = "github.com/google/certificate-transparency/go/x509",
     visibility = ["//visibility:public"],
     deps = [
         "//vendor/github.com/google/certificate-transparency/go/asn1:go_default_library",

vendor/github.com/google/certificate-transparency/go/x509/pkix/BUILD

@@ -3,6 +3,7 @@ load("@io_bazel_rules_go//go:def.bzl", "go_library")
 go_library(
     name = "go_default_library",
     srcs = ["pkix.go"],
+    importpath = "github.com/google/certificate-transparency/go/x509/pkix",
     visibility = ["//visibility:public"],
     deps = ["//vendor/github.com/google/certificate-transparency/go/asn1:go_default_library"],
 )