Support dark mode

[kevnm67]

Issue 🚧

• Checkbox text isn't visible when dark mode is enabled.

• Mac Mojave with dark mode enabled

Current Behavior 🔍

• 'Constructor' and other checkbox text isn't visible.

Steps to Reproduce

1. Run JsonExport using Mojave with dark mode enabled.

Screen shots

[PlutusCat]

You can edit this Main.storybiard

and recompile.

[huabin]

@kevnm67 Hello, I have fixed this and submitted a PR to the developer, and you can use my version from https://github.com/hzb/JSONExport if you don't want to wait, or you can download the application from https://www.dropbox.com/s/20dm3241jdiwq7p/JSONExport.zip?dl=0, thank you.

[kevnm67]

@hzb I'll check it out. Thanks!

[huabin]

@kevnm67 You are welcome. BTW if it works well, please close this issue, if not, please append the error, I will fix.

[kevnm67]

@hzb Just verified the change locally. Looks good. Thoughts on referencing this issue in your PR? (e.g. fixes #124). Github will automagically close this issue once your PR is closed/merged.