Update Screenshot.java

Add possibility to use {index} in the filename of a screen capture like in the original SeleniumLibrary http://robotframework.org/Selenium2Library/Selenium2Library.html#Capture%20Page%20Screenshot

Author: dunand

src/main/java/com/github/markusbernhardt/seleniumlibrary/keywords/Screenshot.java

@@ -114,6 +114,10 @@ protected String normalizeFilename(String filename) {
 		if (filename == null) {
 			screenshotIndex++;
 			filename = String.format("selenium-screenshot-%d.png", screenshotIndex);
+		} else if(filename.contains("{index}")) {
+			screenshotIndex++;
+			filename = filename.replace("{index}", "%d");
+			filename = String.format(filename, screenshotIndex);
 		} else {
 			filename = filename.replace('/', File.separatorChar);
 		}