Usage examples incompatible with neovim >=0.8 (using deprecated $NVIM_LISTEN_ADDRESS)

[dbarnett]

Per https://neovim.io/doc/user/deprecated.html#%24NVIM_LISTEN_ADDRESS, $NVIM_LISTEN_ADDRESS no longer works in neovim 0.8 and newer, so the usage examples here that rely on it are broken.

[dbarnett]

Looks like that just needs to be changed to --listen.