Fix vim hanging forever on exit

[mluts]

During my workday it often happens that when i close vim - it hangs forever, today i dived into the problem and found that when you do {'op': 'close'} with arbitrary session value - nrepl just hangs.

So i came with this solution, it's a bit disrespectful to say something to nrepl server and not waiting for the answer, but it fixes my issue, maybe there is another way to fix that.

How to reproduce the bug:

• Start nrepl
• Connect to this repl from vim
• Restart nrepl
• Connect to this repl from same vim instance
• Exit vim
• ... vim hangs forever

[tpope]

Should be moot.