Minor linter fix
Minor linter fix

Linter regression introduced in #934, see:
https://github.com/kivy/buildozer/pull/934#discussion_r304309602

rnixx/buildozer,rnixx/buildozer,rnixx/buildozer,kivy/buildozer,kivy/buildozer,kivy/buildozer,rnixx/buildozer,kivy/buildozer