Fix issue where opening a file through Windows Explorer causes the save type to be wrong.

[adamgryu]

Hello! I'm not really familiar with nodejs or electron, but I thought I could fix this little bug. Let me know if this isn't the best way to do this!

Bug Reproduction steps:

• Create a .yarn file and save it.
• Close the editor.
• In Windows, double click on the file to open the editor with the file.
• Press Ctrl-S to save.
• Notice the file is saved as JSON even though it has the .yarn file extension.

This was causing import issues in my Yarn Spinner project.

[blurymind]

nice catch! Thanks for fixing this. merged :tada: