Docs : Update common-pitfalls.md with issue 1319

[jy95]

It adds the bug from issue #1319 into the common-pitfalls.md.

[novemberborn]

@jy95 I've pushed some updates. What do you think?

[jy95]

Less text is more simple :)
For the FR translation it should be :

C'est un problème connu. Vous devez mettre vos tests dans un dossier nommé test ou __tests__

[forresst]

@jy95 I note it. I will do the necessary on the French translation when the necessary will have been done on the AVA repository

[novemberborn]

Thanks @jy95!

@forresst I think @jy95 was interested in doing a PR to https://github.com/avajs/ava-docs/blob/master/fr_FR/docs/common-pitfalls.md to reflect the changes here.

[jy95]

@novemberborn I push the PR right now : avajs/ava-docs#45 . No problem for any change, you are free to change whatever you want ^^

[forresst]

Thanks @jy95.