Add missing pt br relative time translation

[joaovitoras]

Summary of changes

Msgid "now" is empty in the relative time translation file, returning english version
I'm having to do the translation inside my application instead of using the translation of the timex

# before 
Timex.Translator.translate("pt_BR", "relative_time", "now")
=> "now"

# now
Timex.Translator.translate("pt_BR", "relative_time", "now")
"agora"

Checklist

• New functions have typespecs, changed functions were updated
• Same for documentation, including moduledocs
• Tests were added or updated to cover changes
• Commits were squashed into a single coherent commit

[coveralls]

Coverage increased (+0.04%) to 71.239% when pulling 4997abe on joaovitoras:missing-pt-br-translation into 6ff35a5 on bitwalker:master.

[ckhrysze]

Thank you for the PR!

[joaovitoras]

Closed without merge? @ckhrysze