Add ScreenSpaceCameraController minimumZoomDistance to externs.

Author: gberaudo

Cesium.externs.js

@@ -2231,6 +2231,12 @@ Cesium.UniformState.prototype.modelViewProjection;
 Cesium.ScreenSpaceCameraController = function() {};
 
 
+/**
+ * @type {number}
+ */
+Cesium.ScreenSpaceCameraController.prototype.minimumZoomDistance;
+
+
 /**
  * @type {boolean}
  */