Add German umlauts to Gugi

**Describe the bug**
German umlauts (Ä,Ö,Ü,ä,ö,ü,ß) aren't contained in Gugi's glyph set and therefore aren't displayed correctly. Can German umlauts be added please to make the font fully compatible with the German language?

**To Reproduce**
Just use an umlaut in a text which has Gugi as font family.

**Expected behavior**
Umlauts should be displayed in Gugi font as other regular letters.

**Screenshots**

**Additional context**
Tested in Chrome but happens in any other browser as well as glyphs for umlauts are missing.