Make it clear in error messages that api-version above 1.13 is also supported

src/main/java/org/bukkit/craftbukkit/legacy/CraftLegacy.java

@@ -113,7 +113,7 @@ public final class CraftLegacy {
     }
 
     public static Item fromLegacyData(Material material, short data) {
-        Preconditions.checkArgument(material.isLegacy(), "fromLegacyData on modern Material. Did you forget to define api-version: 1.13 in your plugin.yml?");
+        Preconditions.checkArgument(material.isLegacy(), "fromLegacyData on modern Material. Did you forget to define a modern (1.13+) api-version in your plugin.yml?");
 
         MaterialData materialData = new MaterialData(material, (byte) data);
 

src/main/java/org/bukkit/craftbukkit/util/Commodore.java

@@ -173,7 +173,7 @@ public class Commodore
                                 Material.valueOf( "LEGACY_" + name );
                             } catch ( IllegalArgumentException ex )
                             {
-                                throw new AuthorNagException( "No legacy enum constant for " + name + ". Did you forget to define api-version: 1.13 in your plugin.yml?" );
+                                throw new AuthorNagException( "No legacy enum constant for " + name + ". Did you forget to define a modern (1.13+) api-version in your plugin.yml?" );
                             }
 
                             super.visitFieldInsn( opcode, owner, "LEGACY_" + name, desc );