Add prettytable hook (#77)

See pyinstaller/pyinstaller#5319.

Author: krellsebastian

news/77.new.rst

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+Add a hook for prettytable which requires its distribution metadata.

src/_pyinstaller_hooks_contrib/hooks/stdhooks/hook-prettytable.py

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+# ------------------------------------------------------------------
+# Copyright (c) 2020 PyInstaller Development Team.
+#
+# This file is distributed under the terms of the GNU General Public
+# License (version 2.0 or later).
+#
+# The full license is available in LICENSE.GPL.txt, distributed with
+# this software.
+#
+# SPDX-License-Identifier GPL-2.0-or-later
+# ------------------------------------------------------------------
+
+from PyInstaller.utils.hooks import copy_metadata
+datas = copy_metadata('prettytable')