Update GroovyExample.groovy

fail to runMod ，since need to import more classes and couldn't create HandlebarsEngine object without argument . And  No signature of method: com.jetdrone.vertx.yoke.GYoke.engine() is applicable for argument types:(java.lang.String, com.jetdrone.vertx.yoke.engine.GroovyTemplateEngine) values: [html, com.jetdr....