Use more gentle way of stoping mining server

[LNow]

Right now when we want to stop mining server we are sending SIGKILL to the process.

Mining-Local-Server/src/nodeCommand.js

Line 146 in 43bc18f

const { stdout, stderr } = child_process.exec(`kill -9 ${PID}`, { shell: true });

I think that instead of killing process "just like that" we should send SIGTERM signal and let process ends gracefully.

[LNow]

Here is perfect explanation why we should use SIGTERM: https://linuxhandbook.com/sigterm-vs-sigkill/