fix tests (just using local gem)

lib/register/instructions/operator_instruction.rb

@@ -0,0 +1,18 @@
+module Register
+
+  class OperatorInstruction < Instruction
+    def initialize source , operator , left , right
+      super(source)
+      @operator = operator
+      @left = left
+      @right = right
+    end
+    attr_reader :left , :right
+
+    def to_s
+      "OperatorInstruction: #{left} #{operator} #{right}"
+    end
+
+  end
+
+end