You cant choose or change how your coworkers behave. Your coworkers may be avoiding you because they they feel that you are embarrassed by your stutter. So they might hesitate to approach you. so here you have to make a brave move and initiate a conversation with your coworkers about your stutter. Let them know that you are aware of it, and you appreciate their understanding. Tell them how it does not affect intelligence or competence. And you have to be the one to approach them and talk to them. Last point, Dont give a shit about what others think about you.