fix: correct writefile bug when choosing multiple languages

[AlextheYounga]

This change corrects an error generated from selecting multiple languages, where it would pass an array into the writeFile command. Now all data passed to writeFile is converted into a string. This is a very small correction, where I just add .toString() to the data being passed to writeFile()

Error encountered

TypeError [ERR_INVALID_ARG_TYPE]: The "data" argument must be of type string or an instance of Buffer, TypedArray, or DataView. Received an instance of Array
    at writeFile (node:fs:2168:5)
    at node:internal/util:364:7
    at new Promise (<anonymous>)
    at writeFile (node:internal/util:350:12)
    at writeFile (/Users/alexyounger/.config/yarn/global/node_modules/gitignore-it/file_utils.js:37:9)
    at /Users/alexyounger/.config/yarn/global/node_modules/gitignore-it/index.js:44:9 {
  code: 'ERR_INVALID_ARG_TYPE'
}

Solution

await writeFile('.gitignore', gitignoreContent.toString())