Dependencies version

Hi Chris

I modified the pubspec.yaml specifying newer dependencies' versions. This is to fix a problem that I had since dart:uri has been removed but logging_handlers was preventing web_ui (which used to rely on dart:ui) to be updated so everything stopped working.

It's the first time that I try a pull request so hope everything works.

Let me know if you want me to change/fix something and do a pull request again. :)

- Daniele