fix the URL sanitizing in reference to Issue #95

Apparently, When "net/url" parses the URL, the url.URL.Path can also be empty if the URL passed is https://something.com instead of https://something.com/. If we observe the curl's verbose messages, we can see that the it prints out * Rebuilt URL to: https://transfer.sh/. This works for general fetches. But for the case in Issue #95 (closed) , It needs to be rebuilt to trailing slash, so it can be sanitized to /filename.