Bump up spotbugs version

Author: zoewangg

pom.xml

@@ -100,7 +100,7 @@
         <unitils.version>3.3</unitils.version>
         <xmlunit.version>1.3</xmlunit.version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <spotbugs.version>3.1.11</spotbugs.version>
+        <spotbugs.version>4.1.4</spotbugs.version>
         <netty-reactive-streams-http.version>2.0.4</netty-reactive-streams-http.version>
         <freemarker.version>2.3.24-incubating</freemarker.version>
         <javapoet.verion>1.13.0</javapoet.verion>