Use String.indexOf() instead of String.contains()

String.indexOf() is char-based and hence faster than general-purpose
String-based String.contains().

Signed-off-by: Robert Varga <nite@hq.sk>

infra/prism/src/main/java/com/evolveum/midpoint/prism/lex/json/yaml/MidpointYAMLGenerator.java

@@ -36,7 +36,7 @@ public void resetTypeId() {
 
 	@Override
 	protected ScalarEvent _scalarEvent(String value, Character style) {
-		if (value.contains("\n")) {
+		if (value.indexOf('\n') != -1) {
 			style = Character.valueOf('|');
 		}