Bump pyowm to latest version

[domcross]

Weather skill's requirements.txt is currently fixed to pyowm==2.6.1 while pyowm is now at version 3.1. OWM introduced some interesting new features that are supported by pyowm 3.x, e.g. One Call API

In case there are specific reasons to stay with pyowm 2.x a version bump to 2.10-LTS should be considered. According to this timeline the pyowm 2.x long-term support will end 05/30/2021 (given that pyowm 3.0 was released on 05/30/2020)

[krisgesling]

Hey there, Chris is working on a big update to this Skill at the moment - including updating the pyowm API version 👍

[emphasize]

seems requirements.txt kept untouched
pyowm==2.6.1

[krisgesling]

Hey @chrisveilleux was this meant to get bumped with the move to the "One Call API"?

[emphasize]

Confusingly i haven't found a bit we're using from pyowm

[chrisveilleux]

I removed pyowm from the skill, but forgot to remove the dependency. A PR 169 addresses this.