update BUILD files

vendor/github.com/mailru/easyjson/buffer/BUILD

@@ -3,6 +3,7 @@ load("@io_bazel_rules_go//go:def.bzl", "go_library")
 go_library(
     name = "go_default_library",
     srcs = ["pool.go"],
+    importpath = "github.com/mailru/easyjson/buffer",
     visibility = ["//visibility:public"],
 )
 

vendor/github.com/mailru/easyjson/jlexer/BUILD

@@ -7,6 +7,7 @@ go_library(
         "error.go",
         "lexer.go",
     ],
+    importpath = "github.com/mailru/easyjson/jlexer",
     visibility = ["//visibility:public"],
 )
 

vendor/github.com/mailru/easyjson/jwriter/BUILD

@@ -3,6 +3,7 @@ load("@io_bazel_rules_go//go:def.bzl", "go_library")
 go_library(
     name = "go_default_library",
     srcs = ["writer.go"],
+    importpath = "github.com/mailru/easyjson/jwriter",
     visibility = ["//visibility:public"],
     deps = ["//vendor/github.com/mailru/easyjson/buffer:go_default_library"],
 )