Merge pull request alibaba#784 from yakolee/master

容器classLoader发生变化时，保证能loadFilterConfig

src/main/java/com/alibaba/druid/filter/FilterManager.java

@@ -61,6 +61,7 @@ public static Properties loadFilterConfig() throws IOException {
         loadFilterConfig(filterProperties, ClassLoader.getSystemClassLoader());
         loadFilterConfig(filterProperties, FilterManager.class.getClassLoader());
         loadFilterConfig(filterProperties, Thread.currentThread().getContextClassLoader());
+        loadFilterConfig(filterProperties, FilterManager.class.getClassLoader());
 
         return filterProperties;
     }