Fix translation of 'Only nickname' in Dutch

Ghost User
2018-10-25T08:24:56+02:00

Closes #753

#### Previous behaviour
Steps to reproduce:

1. Go to profile edit page
2. Change display name
3. Different meaning in EN and NL

#### New behaviour
Steps to validate that it works:

1. Go to profile edit page
2. Change display name
3. Same meaning in EN and NL