Update the documents to use respond over say in response to slash commands

docs/_advanced/context.md

@@ -25,7 +25,7 @@ async function addTimezoneContext({ payload, client, context, next }) {
   await next();
 }
 
-app.command('request', addTimezoneContext, async ({ command, ack, client, context }) => {
+app.command('/request', addTimezoneContext, async ({ command, ack, client, context }) => {
   // Acknowledge command request
   await ack();
   // Get local hour of request

docs/_advanced/ja_context.md

@@ -25,7 +25,7 @@ async function addTimezoneContext({ payload, client, context, next }) {
   await next();
 }
 
-app.command('request', addTimezoneContext, async ({ command, ack, client, context }) => {
+app.command('/request', addTimezoneContext, async ({ command, ack, client, context }) => {
   // コマンドリクエストの確認
   await ack();
   // リクエスト時のローカル時間を取得

docs/_basic/ja_listening_responding_commands.md

@@ -19,10 +19,10 @@ Slack アプリの管理画面でスラッシュコマンドを設定すると
 
 ```javascript
 // この echo コマンドは ただ、その引数を（やまびこのように）おうむ返しする
-app.command('/echo', async ({ command, ack, say }) => {
+app.command('/echo', async ({ command, ack, respond }) => {
   // コマンドリクエストを確認
   await ack();
 
-  await say(`${command.text}`);
+  await respond(`${command.text}`);
 });
 ```

docs/_basic/listening_responding_commands.md

@@ -19,10 +19,10 @@ When configuring commands within your app configuration, you'll continue to appe
 
 ```javascript
 // The echo command simply echoes on command
-app.command('/echo', async ({ command, ack, say }) => {
+app.command('/echo', async ({ command, ack, respond }) => {
   // Acknowledge command request
   await ack();
 
-  await say(`${command.text}`);
+  await respond(`${command.text}`);
 });
 ```