Make saveBeforeClosing synchronous
Make saveBeforeClosing synchronous

Electron v. 6.0 introduced a sort-of breaking change: dialog functions now return promises by default. They used to take a callback function.

The breaking change means there are now explicitly synchronous versions of dialog methods—in this case: showMessageBoxSync.

Refs https://github.com/electron/electron/pull/17054

briandk/transcriptase,briandk/transcriptase