Track extconf.rb and nokogumbo.c
Track extconf.rb and nokogumbo.c

These files shouldn't be ignored. Fix gitignore to track them.

rubys/nokogumbo,grosser/nokogumbo,rubys/nokogumbo,staugaard/nokogumbo,rubys/nokogumbo,rubys/nokogumbo,swills/nokogumbo,swills/nokogumbo,jbotelho2-bb/nokogumbo,grosser/nokogumbo,jbotelho2-bb/nokogumbo,staugaard/nokogumbo