Add `ps` command to Dockerfile image
Intended to clear errors like the following:
Uncaught Exception occured!
Error: spawn ps ENOENT
at Process.ChildProcess._handle.onexit (internal/child_process.js:267:19)
at onErrorNT (internal/child_process.js:469:16)
at processTicksAndRejections (internal/process/task_queues.js:84:21)
Error: spawn ps ENOENT
at Process.ChildProcess._handle.onexit (internal/child_process.js:267:19)
at onErrorNT (internal/child_process.js:469:16)
at processTicksAndRejections (internal/process/task_queues.js:84:21) {
errno: 'ENOENT',
code: 'ENOENT',
syscall: 'spawn ps',
path: 'ps',
spawnargs: [ '-o', 'pid', '--no-headers', '--ppid', 286 ]
}