Clarify java 8 requirement
Clarify java 8 requirement

Summary: Until we're moved to java9, make sure we clarify that java8 is required for buck

Test Plan: Ran in soyweb-local, looked reasonable

Reviewed By: styurin, ttsugriy

fbshipit-source-id: a085189

Addepar/buck,SeleniumHQ/buck,romanoid/buck,LegNeato/buck,facebook/buck,brettwooldridge/buck,brettwooldridge/buck,Addepar/buck,JoelMarcey/buck,facebook/buck,zpao/buck,rmaz/buck,shs96c/buck,shs96c/buck,LegNeato/buck,romanoid/buck,SeleniumHQ/buck,clonetwin26/buck,rmaz/buck,SeleniumHQ/buck,SeleniumHQ/buck,ilya-klyuchnikov/buck,zpao/buck,ilya-klyuchnikov/buck,romanoid/buck,SeleniumHQ/buck,rmaz/buck,JoelMarcey/buck,JoelMarcey/buck,facebook/buck,nguyentruongtho/buck,brettwooldridge/buck,nguyentruongtho/buck,ilya-klyuchnikov/buck,romanoid/buck,shs96c/buck,Addepar/buck,Addepar/buck,rmaz/buck,romanoid/buck,SeleniumHQ/buck,ilya-klyuchnikov/buck,ilya-klyuchnikov/buck,ilya-klyuchnikov/buck,romanoid/buck,nguyentruongtho/buck,Addepar/buck,rmaz/buck,clonetwin26/buck,zpao/buck,clonetwin26/buck,kageiit/buck,clonetwin26/buck,facebook/buck,nguyentruongtho/buck,JoelMarcey/buck,facebook/buck,romanoid/buck,Addepar/buck,rmaz/buck,SeleniumHQ/buck,brettwooldridge/buck,LegNeato/buck,zpao/buck,brettwooldridge/buck,shs96c/buck,brettwooldridge/buck,romanoid/buck,Addepar/buck,kageiit/buck,LegNeato/buck,kageiit/buck,romanoid/buck,ilya-klyuchnikov/buck,clonetwin26/buck,rmaz/buck,clonetwin26/buck,rmaz/buck,JoelMarcey/buck,shs96c/buck,Addepar/buck,JoelMarcey/buck,clonetwin26/buck,Addepar/buck,brettwooldridge/buck,JoelMarcey/buck,JoelMarcey/buck,brettwooldridge/buck,JoelMarcey/buck,romanoid/buck,SeleniumHQ/buck,JoelMarcey/buck,clonetwin26/buck,LegNeato/buck,romanoid/buck,brettwooldridge/buck,brettwooldridge/buck,ilya-klyuchnikov/buck,SeleniumHQ/buck,JoelMarcey/buck,clonetwin26/buck,brettwooldridge/buck,romanoid/buck,romanoid/buck,Addepar/buck,zpao/buck,brettwooldridge/buck,shs96c/buck,Addepar/buck,ilya-klyuchnikov/buck,shs96c/buck,clonetwin26/buck,shs96c/buck,brettwooldridge/buck,kageiit/buck,LegNeato/buck,SeleniumHQ/buck,rmaz/buck,Addepar/buck,LegNeato/buck,LegNeato/buck,clonetwin26/buck,ilya-klyuchnikov/buck,nguyentruongtho/buck,ilya-klyuchnikov/buck,JoelMarcey/buck,facebook/buck,LegNeato/buck,LegNeato/buck,rmaz/buck,clonetwin26/buck,shs96c/buck,shs96c/buck,ilya-klyuchnikov/buck,rmaz/buck,LegNeato/buck,SeleniumHQ/buck,shs96c/buck,nguyentruongtho/buck,shs96c/buck,facebook/buck,kageiit/buck,nguyentruongtho/buck,kageiit/buck,LegNeato/buck,rmaz/buck,SeleniumHQ/buck,LegNeato/buck,kageiit/buck,zpao/buck,SeleniumHQ/buck,shs96c/buck,clonetwin26/buck,rmaz/buck,Addepar/buck,zpao/buck,JoelMarcey/buck,ilya-klyuchnikov/buck