doc: cookbook: Fix encoding of "André".

This is a followup to f8945734.

* doc/guix-cookbook.texi: Encode "André" as UTF-8, not ISO-8859-1.

doc/guix-cookbook.texi

@@ -15,7 +15,7 @@ Copyright @copyright{} 2020 Oleg Pykhalov@*
 Copyright @copyright{} 2020 Matthew Brooks@*
 Copyright @copyright{} 2020 Marcin Karpezo@*
 Copyright @copyright{} 2020 Brice Waegeneire@*
-Copyright @copyright{} 2020 André Batista@*
+Copyright @copyright{} 2020 André Batista@*
 
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 under the terms of the GNU Free Documentation License, Version 1.3 or