Bump internal release version and add missing javadoc

api/src/main/java/me/lucko/luckperms/api/LuckPermsApi.java

@@ -52,6 +52,7 @@ public interface LuckPermsApi {
 
     /**
      * @return the platform LuckPerms is running on
+     * @since 2.7
      */
     PlatformType getPlatformType();
 

common/src/main/java/me/lucko/luckperms/api/implementation/ApiProvider.java

@@ -67,7 +67,7 @@ public class ApiProvider implements LuckPermsApi {
 
     @Override
     public double getApiVersion() {
-        return 2.6;
+        return 2.7;
     }
 
     @Override