watch considers output file as one of the entrypoints

[Swatinem]

With a command line like this:

$ duo -u duo-es6ify index.js -o build -w

I get the following output:

        using : duo-es6ify
     building : index.js
        built : index.js

*when I `touch index.js`:*

     building : index.js
        built : index.js


     building : build/index.js
        built : build/index.js

So I end up with:

• build/index.js
• build/build/index.js