2.1.2 GridItem className not set

[rsmarsh]

In 2.1.2 the className which is added to each GridItem, along with 'dragging' or 'disabled' is no longer functioning due to a jumbled ternary

This can be seen by taking the codesandbox demo from this repo's README, and bumping the react-grid-dnd version number up to 2.1.2, then inspect the div element wrapping each grid item (as seen here). You will see that the div now has a className of 'undefined', and when dragging, the 'dragging' class is not appended

I have created a pull request #28 with an example fix for this.

[loocuu]

Issue is still present, easy to fix
you need to add parenthesis because className conditional statement clears out content that is added before it.
GridItem.tsx line 143

className:
      "GridItem" +
      (isDragging ? " dragging" : "") +
      (!!disableDrag ? " disabled" : "") +
      (className
        ? ` ${className}`
        : ""),

I can create PR