Ctrl+C does not exit cleanly

**Describe the bug**
From the commandline, I have to press Ctrl+C many times to quit gdbgui:

```
$ gdbgui
Opening gdbgui with default browser at http://127.0.0.1:5000
View gdbgui dashboard at http://127.0.0.1:5000/dashboard
exit gdbgui by pressing CTRL+C
^CTraceback (most recent call last):
File "src/gevent/libev/corecext.pyx", line 561, in gevent.libev.corecext.loop.handle_error
File "gevent/hub.py", line 513, in handle_error
File "gevent/hub.py", line 480, in _normalize_exception
KeyboardInterrupt
Exception ignored in: 'gevent.libev.corecext.gevent_handle_error'
Traceback (most recent call last):
File "src/gevent/libev/corecext.pyx", line 561, in gevent.libev.corecext.loop.handle_error
File "gevent/hub.py", line 513, in handle_error
File "gevent/hub.py", line 480, in _normalize_exception
KeyboardInterrupt:

^CTraceback (most recent call last):
File "src/gevent/libev/corecext.pyx", line 561, in gevent.libev.corecext.loop.handle_error
File "gevent/hub.py", line 513, in handle_error
KeyboardInterrupt
Exception ignored in: 'gevent.libev.corecext.gevent_handle_error'
Traceback (most recent call last):
File "src/gevent/libev/corecext.pyx", line 561, in gevent.libev.corecext.loop.handle_error
File "gevent/hub.py", line 513, in handle_error
KeyboardInterrupt:
^CTraceback (most recent call last):
File "src/gevent/libev/corecext.pyx", line 561, in gevent.libev.corecext.loop.handle_error
File "gevent/hub.py", line 487, in handle_error
KeyboardInterrupt
Exception ignored in: 'gevent.libev.corecext.gevent_handle_error'
Traceback (most recent call last):
File "src/gevent/libev/corecext.pyx", line 561, in gevent.libev.corecext.loop.handle_error
File "gevent/hub.py", line 487, in handle_error
KeyboardInterrupt:
^CTraceback (most recent call last):
File "src/gevent/libev/corecext.pyx", line 561, in gevent.libev.corecext.loop.handle_error
File "gevent/hub.py", line 513, in handle_error
KeyboardInterrupt
Exception ignored in: 'gevent.libev.corecext.gevent_handle_error'
Traceback (most recent call last):
File "src/gevent/libev/corecext.pyx", line 561, in gevent.libev.corecext.loop.handle_error
File "gevent/hub.py", line 513, in handle_error
KeyboardInterrupt:
^CTraceback (most recent call last):
File "src/gevent/libev/corecext.pyx", line 561, in gevent.libev.corecext.loop.handle_error
File "gevent/hub.py", line 513, in handle_error
File "gevent/hub.py", line 474, in _normalize_exception
KeyboardInterrupt
Exception ignored in: 'gevent.libev.corecext.gevent_handle_error'
Traceback (most recent call last):
File "src/gevent/libev/corecext.pyx", line 561, in gevent.libev.corecext.loop.handle_error
File "gevent/hub.py", line 513, in handle_error
File "gevent/hub.py", line 474, in _normalize_exception
KeyboardInterrupt:
^CTraceback (most recent call last):
File "src/gevent/libev/corecext.pyx", line 561, in gevent.libev.corecext.loop.handle_error
File "gevent/hub.py", line 487, in handle_error
KeyboardInterrupt
Exception ignored in: 'gevent.libev.corecext.gevent_handle_error'
Traceback (most recent call last):
File "src/gevent/libev/corecext.pyx", line 561, in gevent.libev.corecext.loop.handle_error
File "gevent/hub.py", line 487, in handle_error
KeyboardInterrupt:
^CKeyboardInterrupt
2021-05-18T03:22:26Z
```

**Please complete the following information:**
* OS: Fedora Linux 33
* gdbgui version (`gdbgui -v`): gdbgui_0.14.0.2
* gdb version (`gdb -v`): N/A
* browser [e.g. chrome, safari]: Chrome
* python packages (`pip freeze`): N/A