Use gzip compression for static assets

[nolanlawson]

I noticed that the static JS/CSS assets weren't gzipped. Adding Express compression middleware fixes this (while intelligently skipping the HTML since that's chunked and needs to be streamed).

Here's the "before" on a Nexus 5 throttled to 3G; notice the large JS download time:

And here's the "after":

Great work on Vue! Really love the balance between DX and UX; I wrote a bit about it on Twitter. 😃

[yyx990803]

Thanks for both the PR and the kind words on Twitter :)

[nolanlawson]

Thanks for making Vue. :)