fix: show up an appropriate warning if the target path exists and is …

…non-empty (#570)

packages/create-nuxt-app/lib/cli.js

@@ -1,5 +1,6 @@
 #!/usr/bin/env node
 const path = require('path')
+const fs = require('fs')
 const sao = require('sao')
 const cac = require('cac')
 const chalk = require('chalk')
@@ -33,8 +34,12 @@ cli
     if (cliOptions.info) {
       return showEnvInfo()
     }
+    const files = fs.existsSync(outDir) ? fs.readdirSync(outDir) : []
     console.log()
     console.log(chalk`{cyan create-nuxt-app v${version}}`)
+    if (files.length) {
+      return console.log(chalk.red(`Can't create ${outDir} because there's already a non-empty directory ${outDir} existing in path.`))
+    }
     console.log(chalk`✨  Generating Nuxt.js project in {cyan ${outDir}}`)
 
     const { verbose, answers } = cliOptions