Fix compile error

Author: lucko

spark-fabric/src/main/java/me/lucko/spark/fabric/placeholder/SparkFabricPlaceholderApi.java

@@ -23,6 +23,7 @@
 import com.google.gson.JsonParseException;
 import com.mojang.serialization.JsonOps;
 import eu.pb4.placeholders.api.PlaceholderContext;
+import eu.pb4.placeholders.api.PlaceholderHandler;
 import eu.pb4.placeholders.api.PlaceholderResult;
 import eu.pb4.placeholders.api.Placeholders;
 import me.lucko.spark.common.SparkPlatform;