Dart strings literals have same colour as variables

[petrnymsa]

Hi, first of all, thank you for this amazing theme, however, I've found one little issue and I am not sure how to solve it.

In the .dart files (Flutter framework) a string literal has the same colour as variables or function arguments.

See attached screenshot.

According to theme screenshots, a string literal should be coloured differently than variables.

Is there any simple fix? Thank in advance.