fixed TypeError: Unable to access callee of strict mode function

arguments.callee is used in function checkNodeInserted()

I've got this TypeError because "use strict" doesn't allow arguments.callee anymore. unfortunately.

See: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions_and_function_scope/Strict_mode
»[…] Third, arguments.callee is no longer supported. […]«