Remove spaces from windows installer name

Spaces in the file name get escaped to %20. Then the percent sign gets
escaped again on the way to s3 upload, such that the object name on s3
ends up as %2520. To fix this, we can simply omit spaces from our
artifact names.

// FREEBIE

package.json

@@ -51,6 +51,7 @@
       }
     },
     "win": {
+      "artifactName": "${productName}-Setup_${version}.${ext}",
       "publish": {
         "provider": "s3",
         "region": "us-east-1",