Updated gulp tasks to live-reload on change and fix broken pug paths

[yisraelgrimes]

Hi Andy!
I found your repo while searching for a Pug Static Site-Generator. Noticed your comments about the site not reloading manually when pug changes are saved and since I had just fixed this with another project, I thought I would share my solution with you.
I replaced your live-server package with browser-sync and updated the tasks so that when pug/sass/js are changed, gulp will re-run the tasks like you had set up but will now re-load the browser for you. I seperated the 'watch' task and 'default' task to make sure the watcher runs first and then it runs the server when you run 'default.'

Also, I was getting an error with your 'extends' paths in pug so I fixed that link.

I left your original code in the gulpfile and just commented it out so that you could easily see the changes.

If this isn't the kind of solution you were looking for, feel free to disregard my pull request :)

Have a great day!
-Yisrael