Fixing single file mode

Hi,

I noticed a small problem : when running guard-templates in single file mode, the first time the js file is generated correctly, but when I change any template, the new js file will only contain the changed template. I am suggesting this fix, BUT BE AWARE that I did not test it (I don't have the right environment right now to do that, I can test it next week). So be sure to test this solution before submitting it.

Thank you very much :),