Double slashes in tiles url when map using index.json

[RafalR]

The cause of the error:

https://github.com/urbica/tessella/blob/e5bf3d7c11d42036aec728a659b271db73782d0c/src/server.js#L73

tilesUrl //=>http://localhost:4000/\{z}\{x}\{y}.pbf

When a tile is downloaded, a url is incorrect and it looks that way:

http://localhost:4000//12/2311/1371.pbf
http://localhost:4000//12/2311/1370.pbf

instead

http://localhost:4000/12/2311/1371.pbf
http://localhost:4000/12/2311/1370.pbf