chore: correct filename (#791)

change `prompt.js` to `prompts.js`

Author: yozman

docs/Plugin.md

@@ -205,7 +205,7 @@ module.exports = api => {
 
 #### Prompts for 3rd Party Plugins
 
-3rd party plugins are typically installed manually after a project is already created, and the user will initialize the plugin by calling `vue invoke`. If the plugin contains a `prompt.js` in its root directory, it will be used during invocation. The file should export an array of [Questions](https://github.com/SBoudrias/Inquirer.js#question) that will be handled by Inquirer.js. The resolved answers object will be passed to the plugin's generator as options.
+3rd party plugins are typically installed manually after a project is already created, and the user will initialize the plugin by calling `vue invoke`. If the plugin contains a `prompts.js` in its root directory, it will be used during invocation. The file should export an array of [Questions](https://github.com/SBoudrias/Inquirer.js#question) that will be handled by Inquirer.js. The resolved answers object will be passed to the plugin's generator as options.
 
 Alternatively, the user can skip the prompts and directly initialize the plugin by passing options via the command line, e.g.: