Update proguard plugin to support Java 11 compiler
diff --git a/gson/pom.xml b/gson/pom.xml
index bc5e880..3ecd69a 100644
--- a/gson/pom.xml
+++ b/gson/pom.xml
@@ -19,7 +19,7 @@
     <dependency>
       <groupId>com.github.wvengen</groupId>
       <artifactId>proguard-maven-plugin</artifactId>
-      <version>2.0.14</version>
+      <version>2.3.1</version>
       <scope>test</scope>
     </dependency>
   </dependencies>
@@ -111,7 +111,7 @@
           </execution>
         </executions>
         <configuration>
-          <proguardVersion>6.0.2</proguardVersion>
+          <proguardVersion>6.2.2</proguardVersion>
           <obfuscate>true</obfuscate>
           <injar>test-classes-obfuscated-injar</injar>
           <outjar>test-classes-obfuscated-outjar</outjar>
@@ -126,7 +126,7 @@
           <dependency>
             <groupId>net.sf.proguard</groupId>
             <artifactId>proguard-base</artifactId>
-            <version>6.0.2</version>
+            <version>6.2.2</version>
             <scope>runtime</scope>
           </dependency>
         </dependencies>