Clarify error message

Author: eregon

src/main/ruby/truffleruby/core/truffle/random_operations.rb

@@ -48,7 +48,7 @@ def self.check_float(value)
     end
 
     def self.invalid_argument(limit)
-      raise ArgumentError, "invalid argument - #{limit}"
+      raise ArgumentError, "invalid argument - negative limit: #{limit}"
     end
 
     def self.rand_int(randomizer, limit, restricted)