Expression expected in PhpStorm
In the menu:
PhpStorm > Preferences > Languages & Frameworks > Javascript
You'll see a box that says: JavaScript Language Version.
You should be able to change the option to ECMAScript 6 and apply.
Also:
PhpStorm > Preferences > Editor > File Types Find ECMAScript 6 in the list and add *.vue to the registered patterns list. You could add it to the Javascript file type to for good measure.