Update CommandSpawn.java

Previous: "/pokespawn 
 <bossmode>"
Now: "/pokespawn 
 <bossmode?> <level??>(Ranging from 01 to 99, for 100 it's levelmax instead of level100) <nature:naturename> <size?>(ranging from 0 for pygmy to 6 for enormous)

Examples: 
/pokespawn Charizard level90 boss3 size6 s nature:lax
/pokespawn Mewtwo level1 size0 s nature:Adamant