Update to support core api changes

Author: benwoo1110

src/main/java/org/mvplugins/multiverse/signportals/MultiverseSignPortals.java

@@ -24,11 +24,11 @@
 @Service
 public class MultiverseSignPortals extends MultiversePlugin {
 
+    private static final double TARGET_CORE_API_VERSION = 5.0;
+
     private MultiverseCoreApi core;
     private PluginServiceLocator serviceLocator;
 
-    private final static int requiresProtocol = 50;
-
     /** This fires before I get Enabled. */
     public void onLoad() {
         Logging.init(this);
@@ -96,7 +96,7 @@ public String getVersionInfo() {
     }
 
     @Override
-    public int getTargetCoreProtocolVersion() {
-        return requiresProtocol;
+    public double getTargetCoreVersion() {
+        return TARGET_CORE_API_VERSION;
     }
 }