Fix broken download link (#8800)
Fix broken download link (#8800)

Download link https://prebid.org/download.html no longer valid. Updated with current link https://docs.prebid.org/download.html
ImproveDigital/Prebid.js,HuddledMasses/Prebid.js,prebid/Prebid.js,gumgum/Prebid.js,ImproveDigital/Prebid.js,prebid/Prebid.js,PubWise/Prebid.js,HuddledMasses/Prebid.js,HuddledMasses/Prebid.js,ImproveDigital/Prebid.js,gumgum/Prebid.js,prebid/Prebid.js,gumgum/Prebid.js,PubWise/Prebid.js,PubWise/Prebid.js