fixes #1005

The upstream gcp aggressively closes the connection once it has
received Content-Length bytes. However the @google-cloud/storage
module doesn't handle this well and emits no event in this case.
We were setting Content-Length because it's slightly more
efficient and was important for our download progress
bar (not anymore). The download should function fine without
setting the Content-Length, and allows the storage stream to finish
before closing the upstream socket.

server/storage/gcs.js

@@ -13,7 +13,7 @@ class GCSStorage {
   }
 
   getStream(id) {
-    return this.bucket.file(id).createReadStream();
+    return this.bucket.file(id).createReadStream({ validation: false });
   }
 
   set(id, file) {