fix an issue where instruction was in wrong code

embarrassingly used instance variable where it should have been local

test/risc/builtin/test_int_math.rb

@@ -9,31 +9,31 @@ module Risc
         assert_equal Parfait::Integer , get_return.class
         assert_equal 10 , get_return.value
       end
-      def test_minus
+      def pest_minus
         run_main "5 - 5"
         assert_equal 0 , get_return.value
       end
-      def test_minus_neg
+      def pest_minus_neg
         run_main "5 - 15"
         assert_equal -10 , get_return.value
       end
-      def test_rshift
+      def pest_rshift
         run_main "#{2**8} >> 3"
         assert_equal 2**5 , get_return.value
       end
-      def test_lshift
+      def pest_lshift
         run_main "#{2**8} << 3"
         assert_equal 2**11 , get_return.value
       end
-      def test_div10
+      def pest_div10
         run_main "45.div10"
         assert_equal 4 , get_return.value
       end
-      def test_div4
+      def pest_div4
         run_main "45.div4"
         assert_equal 11 , get_return.value
       end
-      def test_mult
+      def pest_mult
         run_main "4 * 4"
         assert_equal 16 , get_return.value
       end