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%);

After thinking about this a bit more, instead of making preceding whitespace optional, I think we should add option for a colon. This will eliminate false positives for something like `xyz-linear-gradient(...)`. Will that work?