Suppress "unchecked or unsafe operations" warning in JSONConfiguration

On every build, xmlint warned about "unchecked or unsafe operations" in
the JSONConfiguration class, but fixing that would be an API-breaking
change to the OCPP library.

Suppress the warnings, since they cannot be fixed for now.

Author: robert-s-ubi

OCPP-J/src/main/java/eu/chargetime/ocpp/JSONConfiguration.java

@@ -58,11 +58,13 @@ public <T> JSONConfiguration setParameter(String name, T value) {
     return this;
   }
 
+  @SuppressWarnings("unchecked")
   public <T> T getParameter(String name) {
     //noinspection unchecked
     return (T) parameters.get(name);
   }
 
+  @SuppressWarnings("unchecked")
   public <T> T getParameter(String name, T defaultValue) {
     //noinspection unchecked
     T value = (T) parameters.get(name);