Updated Fajr angle for ISNA method

It has come to my attention that ISNA and the Fiqh council of North America recommend 17.5 degrees instead of 15 for the Fajr angle. Source: http://www.icoproject.org/ISNA-Adopts-New-Angles-for-Fajer-and-Isha_ad-id!81-l!en.ks

My testing has shown this to be more accurate for locations in North America and we should adopt this change ASAP.