made path relative to root

Author: tschie

src/main/java/com/esri/samples/map/open_mobile_map_package/OpenMobileMapPackageSample.java

@@ -51,7 +51,7 @@ public void start(Stage stage) throws Exception {
       mapView = new MapView();
 
       //load a mobile map package
-      final String mmpkPath = new File("samples-data/mmpk/Yellowstone.mmpk").getAbsolutePath();
+      final String mmpkPath = new File("./samples-data/mmpk/Yellowstone.mmpk").getAbsolutePath();
       MobileMapPackage mobileMapPackage = new MobileMapPackage(mmpkPath);
 
       mobileMapPackage.loadAsync();