Fix .appveyor.yml link in README.md
Fix .appveyor.yml link in README.md

Someone seems to have forgotten a dot in the URL.
akinwale/lbry-app,lbryio/lbry-electron,lbryio/lbry-app,lbryio/lbry-electron,MaxiBoether/lbry-app,akinwale/lbry-app,MaxiBoether/lbry-app,lbryio/lbry-electron,MaxiBoether/lbry-app,MaxiBoether/lbry-app,akinwale/lbry-app,jsigwart/lbry-app,jsigwart/lbry-app,akinwale/lbry-app,lbryio/lbry-app,jsigwart/lbry-app,jsigwart/lbry-app