feat!: Support Electron 7

[amaury1093]

fixes #243

BREAKING CHANGE:

• Drop support for Electron 4, 5, and 6.
• Remove deprecated passing string argument to menubar, use dir field instead

- menubar('/home/me/MY_ABSOLUTE_PATH');
+ menubar({ dir: '/home/me/MY_ABSOLUTE_PATH' });

• Remove deprecated passing x, y, height, width, alwaysOnTop fields to menubar, pass them instead into the browserWindow field

- menubar({
-   x: 12,
-   y: 34,
-   height: 500,
-   width: 320,
-   alwaysOnTop: true
- });
+ menubar({
+   browserWindow: {
+     x: 12,
+     y: 34,
+     height: 500,
+     width: 320,
+     alwaysOnTop: true
+  }
+ });