Fixed typo (replaced en with én) in relative times for norwegian lang…

…uage.

Hi, Our Norwegian translator reported to us that there is a small typo in the Norwegian translations for relative times.
`en` should be replaced with `én` in expressions like `en time`, `en dag`...

Thanks!

locale/nb.js

@@ -47,13 +47,13 @@
  ss: '%d sekunder',
  m: 'ett minutt',
  mm: '%d minutter',
- h: 'en time',
+ h: 'én time',
  hh: '%d timer',
- d: 'en dag',
+ d: 'én dag',
  dd: '%d dager',
- w: 'en uke',
+ w: 'én uke',
  ww: '%d uker',
- M: 'en måned',
+ M: 'én måned',
  MM: '%d måneder',
  y: 'ett år',
  yy: '%d år',