Status bar error color tokens (#212)

VS Code 1.52 [1] (November 2020) introduced new theme color tokens for
error items in the status bar [2].

The following token have been added to make it more conform with Nord's
style:

- `statusBarItem.errorBackground` - status bar error items background
  color. Error items stand out from other status bar entries to indicate
  error conditions.
- `statusBarItem.errorForeground` - status bar error items foreground
  color. Error items stand out from other status bar entries to indicate
  error conditions.

[1]: https://code.visualstudio.com/updates/v1_52
[2]: https://code.visualstudio.com/updates/v1_52#_new-theme-colors

Co-authored-by: Sven Greb <development@svengreb.de>

Closes GH-203

themes/nord-color-theme.json

@@ -231,6 +231,8 @@
     "statusBarItem.hoverBackground": "#434c5e",
     "statusBarItem.prominentBackground": "#3b4252",
     "statusBarItem.prominentHoverBackground": "#434c5e",
+    "statusBarItem.errorBackground": "#3b4252",
+    "statusBarItem.errorForeground": "#bf616a",
     "statusBar.border": "#3b425200",
     "tab.activeBackground": "#3b4252",
     "tab.activeForeground": "#d8dee9",