Parse negative special durations as negative durations

[gabizou]

Simply put, if you parse strfmt.ParseDuration("-1h"), you will correctly get minus 1 hour. However, when using the "enhanced" durations like d/w, you will not get a negative duration, but a positive one. So strfmt.ParseDuration("-1d") will result in a positive day duration.

[ccoVeille]

I can take a look

[ccoVeille]

I provided a fix