Update English translations to sound more natural

Example texts:

Every hour at every minute(s) past the hour
Every day at every hour:every minute
Every week on every day of the week at every hour:every minute
Every month on every day of the month at every hour:every minute
Every year on every day of the month of every month at every hour:every minute
Merge pull request #13 from mitio/update-english-translations

Update English translations to sound more natural