Bump protocol version

Author: wata727

README.md

@@ -1,6 +1,7 @@
 # TFLint plugin SDK
 [![Build Status](https://github.com/terraform-linters/tflint-plugin-sdk/workflows/build/badge.svg?branch=master)](https://github.com/terraform-linters/tflint-plugin-sdk/actions)
 [![GitHub release](https://img.shields.io/github/release/terraform-linters/tflint-plugin-sdk.svg)](https://github.com/terraform-linters/tflint-plugin-sdk/releases/latest)
+[![go.dev reference](https://img.shields.io/badge/go.dev-reference-007d9c?logo=go&logoColor=white)](https://pkg.go.dev/github.com/terraform-linters/tflint-plugin-sdk)
 [![License: MPL 2.0](https://img.shields.io/badge/License-MPL%202.0-blue.svg)](LICENSE)
 
 [TFLint](https://github.com/terraform-linters/tflint) plugin SDK for building custom rules.
@@ -9,13 +10,15 @@ NOTE: This plugin system is experimental. This means that API compatibility is f
 
 ## Requirements
 
-- TFLint v0.14+
+- TFLint v0.17+
 - Go v1.14
 
 ## Usage
 
 Please refer to [tflint-ruleset-template](https://github.com/terraform-linters/tflint-ruleset-template) for an example plugin implementation using this SDK.
 
+For more details on the API, see [tflint](https://pkg.go.dev/github.com/terraform-linters/tflint-plugin-sdk/tflint) and [helper](https://pkg.go.dev/github.com/terraform-linters/tflint-plugin-sdk/helper) packages on pkg.go.dev.
+
 ## Architecture
 
 This plugin system uses [go-plugin](https://github.com/hashicorp/go-plugin). TFLint launches the plugin as a sub-process and communicates with the plugin over RPC. The plugin acts as a server, while TFLint acts as a client that sends inspection requests to the plugin.

plugin/plugin.go

@@ -10,7 +10,7 @@ import (
 
 // handShakeConfig is used for UX. ProcotolVersion will be updated by incompatible changes.
 var handshakeConfig = plugin.HandshakeConfig{
-	ProtocolVersion:  1,
+	ProtocolVersion:  2,
 	MagicCookieKey:   "TFLINT_RULESET_PLUGIN",
 	MagicCookieValue: "5adSn1bX8nrDfgBqiAqqEkC6OE1h3iD8SqbMc5UUONx8x3xCF0KlPDsBRNDjoYDP",
 }