Linting JSX files (#941)

`.jsx` linting is now in-scope for the `npm run lint` command, and
I linted the base files and some of the viz, there's still quite a bit
of work there, but that's a first pass on it.

caravel/assets/javascripts/dashboard/components/GridLayout.jsx

@@ -90,7 +90,7 @@ class GridLayout extends React.Component {
         rowHeight={100}
         autoSize
         margin={[20, 20]}
-        useCSSTransforms={true}
+        useCSSTransforms
         draggableHandle=".drag"
       >
         {