Add theming color keys for the title bar border
Add theming color keys for the title bar border

Visual Studio Code version 1.15 introduced a new theme color for title
bar borderfor macOS.

It is fully transparent to keep the theme flat.

References:
https://code.visualstudio.com/updates/v1_15#_new-theme-color-for-title-bar-border

GH-46

arcticicestudio/nord-visual-studio-code,arcticicestudio/nord-visual-studio-code