Update src/main/java/com/esri/samples/mapview/scale_bar/README.md
Upadted file extension
<p>Adds a scale bar to visually gauge distances on a map.</p>
-<p><img src="ScaleBar.PNG" alt="Image" /></p>
+<p><img src="ScaleBar.png" alt="Image" /></p>
<h2>How to use the sample</h2>
