Support Neovim

When launching Neovim with this plugin installed, I receive the error vim-jdb: Vim not compiled with job support, vim-jdb requires job. Neovim has job support by default, so it should be compatible with this plugin.

The main thing that would need to change is that the line

if !has('job')

should be updated to

if !(has('job') || has('nvim'))

The job control calls may also need to be updated, but I don't know the specific differences between the two API's offhand.