revert all changes about bump language level, adapt PAPIP with Java8

Author: Ghost-chu

src/main/java/org/maxgamer/quickshop/util/language/text/postprocessing/impl/PlaceHolderApiProcessor.java

@@ -11,9 +11,9 @@
 public class PlaceHolderApiProcessor implements PostProcessor {
     @Override
     public @NotNull String process(@NotNull String text, @Nullable CommandSender sender, String... args) {
-        if(sender instanceof OfflinePlayer player) {
+        if(sender instanceof OfflinePlayer) {
             if (Bukkit.getPluginManager().isPluginEnabled("PlaceHolderAPI")) {
-                return PlaceholderAPI.setPlaceholders(player,text);
+                return PlaceholderAPI.setPlaceholders((OfflinePlayer) sender,text);
             }
         }
         return text;