made whitespace character optional

Addresses #8028 - Quick View doesn't recognize linear-gradient if no space before it

Updated regex to make whitespace character optional before "linear" or "radial"

    // Quick View Always Worked for this
    background : linear-gradient(to bottom, black 0%, white 100%);
    background : radial-gradient(to bottom, black 0%, white 100%);
    background: linear-gradient(to bottom, black 0%, white 100%);
    background: radial-gradient(to bottom, black 0%, white 100%);
    
    // Now this Works Too
    background :linear-gradient(to bottom, black 0%, white 100%);
    background :radial-gradient(to bottom, black 0%, white 100%);

I think I understand.  So the character preceding `linear-gradient` could be colon or whitespace?