update mockito testing dependency
diff --git a/pom.xml b/pom.xml
index f185294..9aad6d9 100644
--- a/pom.xml
+++ b/pom.xml
@@ -147,7 +147,7 @@
         <dependency>
             <groupId>org.mockito</groupId>
             <artifactId>mockito-core</artifactId>
-            <version>2.21.0</version>
+            <version>3.1.0</version>
             <scope>test</scope>
         </dependency>
         <dependency>