update package.ps1 to use $(Build.BuildNumber)
update package.ps1 to use $(Build.BuildNumber)

The Build number format is now specified in the Build Definition
and is a supplied parameter.

Vedin/corefxlab,VSadov/corefxlab,ericstj/corefxlab,VSadov/corefxlab,VSadov/corefxlab,benaadams/corefxlab,KrzysztofCwalina/corefxlab,weshaggard/corefxlab,dotnet/corefxlab,VSadov/corefxlab,Vedin/corefxlab,adamsitnik/corefxlab,ericstj/corefxlab,benaadams/corefxlab,tarekgh/corefxlab,tarekgh/corefxlab,stephentoub/corefxlab,ericstj/corefxlab,Vedin/corefxlab,ahsonkhan/corefxlab,KrzysztofCwalina/corefxlab,stephentoub/corefxlab,Vedin/corefxlab,alexperovich/corefxlab,ericstj/corefxlab,joshfree/corefxlab,ahsonkhan/corefxlab,ericstj/corefxlab,whoisj/corefxlab,adamsitnik/corefxlab,stephentoub/corefxlab,stephentoub/corefxlab,dotnet/corefxlab,ericstj/corefxlab,stephentoub/corefxlab,VSadov/corefxlab,whoisj/corefxlab,Vedin/corefxlab,Vedin/corefxlab,hanblee/corefxlab,joshfree/corefxlab,hanblee/corefxlab,stephentoub/corefxlab,VSadov/corefxlab