Adds the InvalidSkillException import to the PapiExpansion class.

- This import is necessary for handling potential exceptions related to invalid skill references within the PlaceholderAPI expansion.

Author: hudsonandres

src/main/java/com/gmail/nossr50/placeholders/PapiExpansion.java

@@ -1,6 +1,7 @@
 package com.gmail.nossr50.placeholders;
 
 import com.gmail.nossr50.api.ExperienceAPI;
+import com.gmail.nossr50.api.exceptions.InvalidSkillException;
 import com.gmail.nossr50.config.experience.ExperienceConfig;
 import com.gmail.nossr50.datatypes.database.PlayerStat;
 import com.gmail.nossr50.datatypes.party.Party;