adding capital letter sharp S and ISO-8859-15 (#222)

adding capital letter sharp S and ISO-8859-15 to german section in languages.py
https://en.wikipedia.org/wiki/Capital_ẞ 
https://en.wikipedia.org/wiki/German_orthography#Alphabet

Co-authored-by: Dan Blanchard <dan.blanchard@gmail.com>

chardet/metadata/languages.py

@@ -111,8 +111,8 @@ def __repr__(self):
         name="German",
         iso_code="de",
         use_ascii=True,
-        charsets=["ISO-8859-1", "WINDOWS-1252"],
-        alphabet="äöüßÄÖÜ",
+        charsets=["ISO-8859-1", "ISO-8859-15", "WINDOWS-1252"],
+        alphabet="äöüßẞÄÖÜ",
         wiki_start_pages=["Wikipedia:Hauptseite"],
     ),
     "Greek": Language(