Change registration start time format from hh:m to hh:mm

Gijs Hendriksen
2018-04-09T11:08:20+02:00

#### Previous behaviour
The time format for the start of registrations was `hh:m`

Steps to reproduce:

1. Go to an event for which registration has not yet opened.
2. Notice it states "Registration will open hh:m"

#### New behaviour
The time format for the start of registrations is `hh:mm`

Steps to validate that it works:

1. Go to an event for which registration has not yet opened.
2. Notice it states "Registration will open hh:mm"