fix: generate snapshot for default behavior

Author: jamesgeorge007

e2e/index.js

@@ -7,6 +7,6 @@ const test = require('ava');
 const rootCommand = path.join(process.cwd(), 'bin/docsify');
 
 test('shows up help message without any args', async t => {
-  const { stdout } = await execa(rootCommand, {reject: false});
-  t.snapshot(stdout);
+    const { stderr } = await execa(rootCommand, {reject: false});
+    t.snapshot(stderr)
 });

e2e/index.js.md

@@ -8,4 +8,22 @@ Generated by [AVA](https://ava.li).
 
 > Snapshot 1
 
-    ''
+    `Usage: docsify <init|serve> <path>␊
+    ␊
+    Commands:␊
+      docsify init [path]   Creates new docs␊
+      docsify serve [path]  Run local server to preview site.␊
+      docsify start <path>  Server for SSR␊
+    ␊
+    Global Options␊
+      --help, -h     Show help                                             [boolean]␊
+      --version, -v  Show version number                                   [boolean]␊
+    ␊
+    Documentation:␊
+      https://docsifyjs.github.io/docsify␊
+      https://docsifyjs.github.io/docsify-cli␊
+    ␊
+    Development:␊
+      https://github.com/docsifyjs/docsify-cli/blob/master/CONTRIBUTING.md␊
+    ␊
+    [ERROR] 0 arguments passed. Please specify a command`