Fix french translation

[ethicnology]

I fixed some french sentences and bad translations.
e.g : Evoyer (which mean nothing in french) to Envoyer (which mean Send)

[hebasto]

@ethicnology https://github.com/bitcoin/bitcoin/blob/master/doc/translation_process.md

[maflcko]

Thanks for helping with translations! However, changes to translations as well as new translations are submitted to Bitcoin Core's Transifex page.

Translations are periodically pulled from Transifex and merged into the git repository. See the translation process for details on how this works. So we do not accept translation changes as GitHub pull requests because the next pull from Transifex would automatically overwrite them again.