Better type definition

Fixes the `Invalid type(s) for operator IN.` warnings from the closure compiler.

src/ol/interaction/Modify.js

@@ -223,7 +223,7 @@ const Modify = function(options) {
   /**
   * @const
   * @private
-  * @type {Object.<string, function(ol.Feature, ol.geom.Geometry)>}
+  * @type {!Object.<string, function(ol.Feature, ol.geom.Geometry)>}
   */
   this.SEGMENT_WRITERS_ = {
     'Point': this.writePointGeometry_,

src/ol/interaction/Pointer.js

@@ -97,7 +97,7 @@ const PointerInteraction = function(opt_options) {
   this.handlingDownUpSequence = false;
 
   /**
-   * @type {Object.<string, ol.pointer.PointerEvent>}
+   * @type {!Object.<string, ol.pointer.PointerEvent>}
    * @private
    */
   this.trackedPointers_ = {};

src/ol/interaction/Snap.js

@@ -97,7 +97,7 @@ const Snap = function(opt_options) {
    * If a feature geometry changes while a pointer drag|move event occurs, the
    * feature doesn't get updated right away.  It will be at the next 'pointerup'
    * event fired.
-   * @type {Object.<number, ol.Feature>}
+   * @type {!Object.<number, ol.Feature>}
    * @private
    */
   this.pendingFeatures_ = {};