kivy: fix app not even starting
kivy: fix app not even starting

```
  File "/home/user/venvs/electrum37/lib64/python3.7/site-packages/kivy/lang/builder.py", line 654, in _apply_rule
    child = cls(__no_builder=True)
TypeError: __init__() got an unexpected keyword argument '__no_builder'
```

follow-up c70484455c561b53664ba349cb88587bc349efc9

pooler/electrum-ltc,pooler/electrum-ltc,spesmilo/electrum,pooler/electrum-ltc,wakiyamap/electrum-mona,spesmilo/electrum,spesmilo/electrum,wakiyamap/electrum-mona,wakiyamap/electrum-mona,pooler/electrum-ltc,spesmilo/electrum,wakiyamap/electrum-mona