update async-http-client to 1.9.31 (#88)
update async-http-client to 1.9.31 (#88)

christ66/zendesk-java-client,gvh1234/zendesk-java-client,norrisjeremy/zendesk-java-client,cloudbees/zendesk-java-client,ydubreuil/zendesk-java-client,matthewtckr/zendesk-java-client