Weber does not compile correctly against Elixir 1.0+

There are 2 dependencies that seem to be broket
jsex  - project was renamed
plug - 0.5.0/0.6.0  use nil?  which was changed to is_nil in Elixir 1.0

After updating these 2 deps I was able to do mix deps.get, compile without issues, however it does look like most of the tests are broken.  

I have submitted a pull request for above changes. 
