fixed image extensions to work with sample viewer

Author: tschie

src/main/java/com/esri/samples/featurelayers/feature_collection_layer/FeatureCollectionLayer.PNG renamed to src/main/java/com/esri/samples/featurelayers/feature_collection_layer/FeatureCollectionLayer.png

@@ -2,7 +2,7 @@
 
 <p>Demonstrates how to create a new Feature Collection with a Point, Polyline, and Polygon Feature Collection Table. The Feature Collection is then displayed on the ArcGISMap as a Layer.</p>
 
-<p><img src="FeatureCollectionLayer.PNG"/></p>
+<p><img src="FeatureCollectionLayer.png"/></p>
 
 <h2>How it works</h2>
 

src/main/java/com/esri/samples/featurelayers/feature_collection_layer/README.md

@@ -2,7 +2,7 @@
 
 <p>Demonstrates how to consume an Esri Geodatabase by using a FeatureLayer and a GeodatabaseFeatureTable.</p>
 
-<p><img src="FeatureLayerGeodatabase.PNG"/></p>
+<p><img src="FeatureLayerGeodatabase.png"/></p>
 
 <h2>How it works</h2>
 

src/main/java/com/esri/samples/featurelayers/feature_layer_geodatabase/FeatureLayerGeodatabase.PNG renamed to src/main/java/com/esri/samples/featurelayers/feature_layer_geodatabase/FeatureLayerGeodatabase.png

@@ -2,7 +2,7 @@
 
 <p>Demonstrates how to export a section of the ArcGISMap as an image file.</p>
 
-<p><img src="TakeScreenShot.PNG"/></p>
+<p><img src="TakeScreenShot.png"/></p>
 
 <h2>How to use this Sample</h2>