Handle disconnections accordingly

[mattborghi]

Especially when users log out:

JULIA Server: 
signal (15): Terminated
in expression starting at /home/borghi/Desktop/Matias/umc/monaco-editor-julia-language-server/server/lib/server.jl:55

JULIA Server: epoll_pwait at /lib/x86_64-linux-gnu/libc.so.6 (unknown line)

JULIA Server: uv__io_poll at /workspace/srcdir/libuv/src/unix/linux-core.c:270

JULIA Server: uv_run at /workspace/srcdir/libuv/src/unix/core.c:359

JULIA Server: jl_task_get_next at /buildworker/worker/package_linux64/build/src/partr.c:473

JULIA Server: poptask at ./task.jl:704

JULIA Server: wait at ./task.jl:712 [inlined]
wait at ./condition.jl:106

JULIA Server: take_buffered at ./channels.jl:387

JULIA Server: take! at ./channels.jl:381 [inlined]
iterate at ./channels.jl:448

JULIA Server: macro expansion at /home/borghi/.julia/packages/JSONRPC/1Kq3H/src/core.jl:94 [inlined]
#1 at ./task.jl:356
unknown function (ip: 0x7fed44cbe27c)

JULIA Server: _jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2231 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2398

JULIA Server: jl_apply at /buildworker/worker/package_linux64/build/src/julia.h:1690 [inlined]
start_task at /buildworker/worker/package_linux64/build/src/task.c:707
unknown function (ip: (nil))

JULIA Server: unknown function (ip: (nil))
Allocations: 31666406 (Pool: 31656852; Big: 9554); GC: 31