Fix the support of MQTT with java8 (apache#14968)

Author: HTHou

pom.xml

@@ -81,7 +81,8 @@
         <google.java.format.version>1.22.0</google.java.format.version>
         <gson.version>2.10.1</gson.version>
         <guava.version>32.1.2-jre</guava.version>
-        <h2.version>2.3.232</h2.version>
+        <!-- This was the last version to support Java 8 -->
+        <h2.version>2.2.224</h2.version>
         <httpclient.version>4.5.14</httpclient.version>
         <httpcore.version>4.4.16</httpcore.version>
         <!--