Tweak pyup.io parameters

Automate boring stuff we had to manually do on every PR like:

• add the good label
• rename the commit name with the good ticket

Also we can prefix the branch name to prevent tests to be ran.

Typically, we have to have those lines to the .pyup.xml file:

pr_prefix: "NXDRIVE-1142: Upgrade "
label_prs: dependencies
branch_prefix: wip-

Informations at https://pyup.io/docs/bot/config/.