Update england_current(), england data

[JoGall]

2018/19 season data from http://www.football-data.co.uk/englandm.php is now dd/mm/yyyy format instead of dd/mm/yy as in previous seasons, so code for england_current(2018) was broken.

• Updated england_current() to conditionally format date depending on whether before or after 2018 season. Season argument defaults to 2018 instead of 2017.
• Updated england dataframe to include 2017/18 season. Only need to run rbind(england, england_current()) now to have all fixtures up to date.

[jalapic]

thank you Joe - I really appreciate all your help with this.