docs(zh): fix SyntaxError + = => += (#6147)[skip ci]

shooterRao · web-flow · commit ced2c34998b7 · 2020-12-15T12:15:50.000+08:00
lines[renderIndex] + = `\n router,` =&gt; lines[renderIndex] += `\n router,`
diff --git a/docs/zh/dev-guide/plugin-dev.md b/docs/zh/dev-guide/plugin-dev.md
@@ -268,7 +268,7 @@ module.exports.hooks = (api) => {
     const lines = contentMain.split(/\r?\n/g)
 
     const renderIndex = lines.findIndex(line => line.match(/render/))
-    lines[renderIndex] + = `\n router,`
+    lines[renderIndex] += `\n router,`
   })
 }
 ```

Original file line number	Diff line number	Diff line change
`@@ -268,7 +268,7 @@ module.exports.hooks = (api) => {`
`268`	`268`	`const lines = contentMain.split(/\r?\n/g)`
`269`	`269`
`270`	`270`	`const renderIndex = lines.findIndex(line => line.match(/render/))`
`271`		- lines[renderIndex] + = `\n router,`
	`271`	+ lines[renderIndex] += `\n router,`
`272`	`272`	`})`
`273`	`273`	`}`
`274`	`274`	```