fix alert property utils init properties. (#4527)

dolphinscheduler-alert/src/main/java/org/apache/dolphinscheduler/alert/utils/PropertyUtils.java

@@ -43,6 +43,11 @@ public class PropertyUtils {
 
     private static final Properties properties = new Properties();
 
+    /**
+     *  init properties
+     */
+    private static final PropertyUtils propertyUtils = new PropertyUtils();
+
     private PropertyUtils() {
         init();
     }

dolphinscheduler-alert/src/main/resources/alert.properties

@@ -22,7 +22,7 @@
 
 #alert.plugin.dir config the Alert Plugin dir . AlertServer while find and load the Alert Plugin Jar from this dir when deploy and start AlertServer on the server .
 #eg :
-alert.plugin.dir=/opt/soft/spi/lib/plugin/alert
+#alert.plugin.dir=/opt/soft/spi/lib/plugin/alert
 
 #maven.local.repository=/Users/gaojun/Documents/jianguoyun/localRepository