fix typo in readme.txt
fix typo in readme.txt

bigfatbrowncat/avian-pack.avian,joshuawarner32/avian,lwahlmeier/avian,minor-jason/avian,ucdseniordesign/avian,MaartenR/avian,getlantern/avian,ucdseniordesign/avian,badlogic/avian,lostdj/avian,lwahlmeier/avian,badlogic/avian,MaartenR/avian,dicej/avian,lostdj/avian,bgould/avian,lostdj/avian,marcinolawski/avian,lostdj/avian,joshuawarner32/avian,dicej/avian,getlantern/avian,minor-jason/avian,MaartenR/avian,marcinolawski/avian,joshuawarner32/avian,bigfatbrowncat/avian-pack.avian,ucdseniordesign/avian,minor-jason/avian,marcinolawski/avian,lwahlmeier/avian,dicej/avian,bigfatbrowncat/avian-pack.avian,lwahlmeier/avian,getlantern/avian,badlogic/avian,minor-jason/avian,joshuawarner32/avian,dicej/avian,bigfatbrowncat/avian-pack.avian,ucdseniordesign/avian,bgould/avian,bgould/avian,getlantern/avian,marcinolawski/avian,MaartenR/avian,bgould/avian,badlogic/avian