Merge pull request CesiumGS#7064 from OmarShehata/fix-doc-typo

Fix typo in docs

Author: Hannah

Source/Widgets/Viewer/Viewer.js

@@ -1285,7 +1285,7 @@ Either specify options.terrainProvider instead or set options.baseLayerPicker to
             }
         },
         /**
-         * Gets the event that is raised when the selected entity chages
+         * Gets the event that is raised when the selected entity changes.
          * @memberof Viewer.prototype
          * @type {Event}
          * @readonly
@@ -1296,7 +1296,7 @@ Either specify options.terrainProvider instead or set options.baseLayerPicker to
             }
         },
         /**
-         * Gets the event that is raised when the tracked entity chages
+         * Gets the event that is raised when the tracked entity changes.
          * @memberof Viewer.prototype
          * @type {Event}
          * @readonly