Bump Deps

[Steven Holdsworth]

mix hex.outdated

Dependency               Current  Latest  Update possible
chrome_remote_interface  0.1.0    0.2.0   No
cowboy                   1.1.2    2.6.3   No
erlexec                  1.9.5    1.10.0  No
ex_doc                   0.19.3   0.20.2  Yes
exexec                   0.1.0    0.2.0   Yes
jason                    1.1.2    1.1.2
plug                     1.7.2    1.8.0   Yes
plug_cowboy              1.0.0    2.0.2   No

This should be split into 3.

1. Low risk (jason, ex_doc, chrome_remote_interface)
2. Native Port Drivers (erl_exec, exexec)
3. Plug & Cowboy