add .gitattributes and fix prettier/js warnings (#3094)

see title, as discussed in
https://github.com/MichMich/MagicMirror/pull/3093

js/check_config.js

@@ -18,7 +18,6 @@ const Utils = require(`${rootPath}/js/utils.js`);
 /**
  * Returns a string with path of configuration file.
  * Check if set by environment variable MM_CONFIG_FILE
- *
  * @returns {string} path and filename of the config file
  */
 function getConfigFile() {