Fix variable name

lib/rubygems-requirements-system/platform/base.rb

@@ -118,7 +118,7 @@ def run_command_line(package, action, command_line)
           alert_warning("'#{package}' system package is required.")
           alert_warning("Run the following command " +
                         "to #{action} required system package: " +
-                        escaped_install_command.join(" "))
+                        escaped_command.join(" "))
         end
         succeeded
       end