Update GNU Fortran documentation (7.3.0)

lib/docs/scrapers/gnu/gnu_fortran.rb

@@ -7,7 +7,7 @@ module Docs
     }
 
     version '7' do
-      self.release = '7.2.0'
+      self.release = '7.3.0'
       self.dir = '/Users/Thibaut/DevDocs/Docs/gfortran7'
       self.base_url = "https://gcc.gnu.org/onlinedocs/gcc-#{release}/gfortran/"
     end