Added Michael Frey to AUTHORS file.
@@ -238,3 +238,4 @@ Kevin Falcone <kevin@edx.org>
Mirjam Škarica <mirjamskarica@gmail.com>
Saleem Latif <saleem@edx.org>
Julien Paillé <julien.paille@openfun.fr>
Michael Frey <mfrey@edx.org>
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