CMS7-7672 remove printing stacktrace and fix typo

src/main/java/org/onehippo/cms7/services/eventbus/GuavaEventBusListenerProxy.java

@@ -56,7 +56,6 @@ public abstract class GuavaEventBusListenerProxy implements Cloneable {
             } catch (IllegalAccessException e) {
                 throw new Error("Method became inaccessible: " + event, e);
             } catch (InvocationTargetException e) {
-                e.printStackTrace();
                 if (e.getCause() instanceof Error) {
                     throw (Error) e.getCause();
                 }

src/main/java/org/onehippo/cms7/services/eventbus/GuavaEventBusListenerProxyFactory.java

@@ -61,7 +61,7 @@ import org.slf4j.LoggerFactory;
  *   registered.
  * </p>
  * <p>
- *   Such a proxy class is only generated ones for each listener class and reused if more than one listener (class)
+ *   Such a proxy class is only generated once for each listener class and reused if more than one listener (class)
  *   instance is registered on the {@link GuavaHippoEventBus}, in which case an existing proxy instance is
  *   {@link org.onehippo.cms7.services.eventbus.GuavaEventBusListenerProxy#clone(Object) cloned}
  *   with the new listener instance injected.