Set the background to "default" instead of BackgroundColor #37
Description
As of Windows 10 build 18298, the new “Terminal” settings allow setting default ForegroundColor and BackgroundColor values which are separate from the 16 color "ConsoleColor" palette.
PowerLine doesn't use the ANSI/VT escape sequence for default as the default background, but instead specified $Host.UI.RawUI.BackgroundColor -- which no longer matches the actual background color if the user sets the terminal settings.