Error using the source bundle

The unminified Rollup bundle [dist/L.Control.Heightgraph.js](https://github.com/GIScience/Leaflet.Heightgraph/blob/master/dist/L.Control.Heightgraph.js) has the dependencies in global scope. The [module wrapper](https://github.com/GIScience/Leaflet.Heightgraph/blob/9e45353ae01e4389124701bdacb62ee255d3fec1/dist/L.Control.Heightgraph.js#L4607-L4623) only encloses the plugin itself.

Loading this source bundle directly leads to an error, see http://plnkr.co/edit/SZzWSpopCELzDcgu?preview (see Console):
```
Uncaught TypeError: Cannot set property top of # which has only a getter
at L.Control.Heightgraph.js:3993
```
Concatenating it with the BRouter-Web dependencies e.g. leads to a conflict with Turf.js, see [#101 (comment)](https://github.com/GIScience/Leaflet.Heightgraph/issues/101#issuecomment-716077109).

The mininfied bundle [dist/L.Control.Heightgraph.min.js](https://github.com/GIScience/Leaflet.Heightgraph/blob/master/dist/L.Control.Heightgraph.min.js) works, as it is enclosed in an IIFE (immediately invoked function expression):
```
!function(){ ... }();
```

So it would be great if the source bundle could be enclosed in an IIFE as well or the module wrapper moved to the top.