Follow 301 redirects in the bash script that downloads the models

[jkremser]

Fixes #143

[jspitzen]

Isn't the underlying issue here that the files are no longer accessible through http, but only https? imo, altering the BASE_URL to BASE_URL="https://cs.stanford.edu/people/jcjohns/fast-neural-style/models/" is a better solution than following the 301

[jwittenbach]

I can confirm that simply switching the base URL to use HTTPS instead of HTTP does work. However, updating the curl commands to follow redirects is probably also good in case the files move again.