Add changelog for OkHttp 3.12.2.
Add changelog for OkHttp 3.12.2.

tiarebalbi/okhttp,cmzy/okhttp,square/okhttp,ansman/okhttp,ze-pequeno/okhttp,ze-pequeno/okhttp,square/okhttp,cketti/okhttp,cmzy/okhttp,cketti/okhttp,yschimke/okhttp,ansman/okhttp,cketti/okhttp,ze-pequeno/okhttp,yschimke/okhttp,tiarebalbi/okhttp,ansman/okhttp,square/okhttp,yschimke/okhttp,tiarebalbi/okhttp