Update changelog dates docs/api/covidcast_changelog.md
Update changelog dates docs/api/covidcast_changelog.md
cmu-delphi/delphi-epidata,cmu-delphi/delphi-epidata,cmu-delphi/delphi-epidata,cmu-delphi/delphi-epidata,cmu-delphi/delphi-epidata,cmu-delphi/delphi-epidata