Fix uploadcdn for local build

bin/upload-to-cdn.js

@@ -103,7 +103,7 @@ async function main (packageName, version) {
   // version should only be a positional arg and semver string
   // this deals with usage like `npm run uploadcdn uppy -- --force`
   // where we force push a local build
-  if (version.startsWith('-')) version = undefined
+  if (version && version.startsWith('-')) version = undefined
 
   const s3 = new AWS.S3({
     credentials: new AWS.Credentials({