Update changelog for 3.1.1.
Update changelog for 3.1.1.

mjbenedict/okhttp,cmzy/okhttp,zmarkan/okhttp,tiarebalbi/okhttp,rschilling/okhttp,NightlyNexus/okhttp,square/okhttp,qingsong-xu/okhttp,tiarebalbi/okhttp,yschimke/okhttp,SunnyDayDev/okhttp,tiarebalbi/okhttp,Synix/okhttp,qingsong-xu/okhttp,cnoldtree/okhttp,mjbenedict/okhttp,Voxer/okhttp,hgl888/okhttp,rschilling/okhttp,yakatak/okhttp,square/okhttp,cnoldtree/okhttp,nfuller/okhttp,ansman/okhttp,Synix/okhttp,cmzy/okhttp,ansman/okhttp,ze-pequeno/okhttp,artem-zinnatullin/okhttp,cnoldtree/okhttp,NightlyNexus/okhttp,jrodbx/okhttp,ansman/okhttp,hgl888/okhttp,cketti/okhttp,Voxer/okhttp,nfuller/okhttp,SunnyDayDev/okhttp,germanattanasio/okhttp,rschilling/okhttp,jrodbx/okhttp,wfxiang08/okhttp,germanattanasio/okhttp,zmarkan/okhttp,wfxiang08/okhttp,yakatak/okhttp,germanattanasio/okhttp,jrodbx/okhttp,yschimke/okhttp,ze-pequeno/okhttp,ze-pequeno/okhttp,Synix/okhttp,qingsong-xu/okhttp,cketti/okhttp,wfxiang08/okhttp,cketti/okhttp,yakatak/okhttp,artem-zinnatullin/okhttp,zmarkan/okhttp,Voxer/okhttp,hgl888/okhttp,NightlyNexus/okhttp,nfuller/okhttp,yschimke/okhttp,SunnyDayDev/okhttp,mjbenedict/okhttp,artem-zinnatullin/okhttp,square/okhttp