Bump test dependencies

Author: acogoluegnes

pom.xml

@@ -61,9 +61,9 @@
     <gson.version>2.8.6</gson.version>
     <logback.version>1.2.3</logback.version>
     <jetty.version>9.4.26.v20200117</jetty.version>
-    <junit.jupiter.version>5.5.2</junit.jupiter.version>
-    <mockito.version>3.2.0</mockito.version>
-    <assertj.version>3.14.0</assertj.version>
+    <junit.jupiter.version>5.6.0</junit.jupiter.version>
+    <mockito.version>3.2.4</mockito.version>
+    <assertj.version>3.15.0</assertj.version>
     <commons-lang3.version>3.9</commons-lang3.version>
     <jmh.version>1.21</jmh.version>