fix label loading in arm

was still loading the integer address
instead of the return address's address
Hello World working

lib/risc/position/position.rb

@@ -147,7 +147,7 @@ module Risc
     end
 
     def self.set?(object)
-      self.positions.has_key?(object)
+      self.positions[object]
     end
 
     # get a position from the cache (object -> position)