Incompatible with Mechjeb 2.15

Seems like the new version changed some stuff we depended on.

```
29615 [ERR 23:50:37.984] [RasterPropMonitor]: Exception initializing JSIMechJeb: System.NotImplementedException: mjCoreTarget
29616   at JSI.JSIMechJeb..cctor () [0x000ce] in <8a42ee704a9c497dbeff9dd86000f1f8>:0 
```