ci: install nodejs 8 in Appveyor, Travis
provider: check node version for debug support
Resolve https://github.com/neovim/neovim/pull/7577#issuecomment-350590592 for Unix.
provider: test if nodejs in ci supports --inspect-brk
nodejs host for neovim requires nodejs 6+ to work properly.
nodejs 6.12+ or 7.6+ is required for debug support via `node --inspect-brk`.
provider: run cli.js of nodejs host directly
npm shims are useless because the user cannot set node to debug mode via
--inspect-brk. This is problematic on Windows which use batchfiles and
shell scripts to compensate for not supporting shebang.
The patch uses `npm root -g` to get the absolute path of the global npm
modules. If that fails, then the user did not install neovim npm package
globally. Use that absolute path to find `neovim/bin/cli.js`, which is
what the npm shim actually runs with node. glob() is for a simple file
check in case bin/ is removed because the npm shims are ignored now.
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