[Firefox] Fixed warning

was getting the warning

canvas: an attempt to set strokeStyle or fillStyle to a value that is neither a string, a CanvasGradient, or a CanvasPattern was ignored.
    
this.context.fillStyle = this.innerColor;


line 66

this pull request fixes the issue, the issue was that fillStyle in firefox expected a string if coming from a function and not a function object outputting a string :/ firefox