Fix Plural-Forms gettext header for Catalan

Signed-off-by: Maxime Petazzoni <maxime.petazzoni@bulix.org>

locale/ca/LC_MESSAGES/ocitysmap.po

@@ -15,7 +15,7 @@ msgstr ""
 "Content-Type: text/plain; charset=utf-8\n"
 "Content-Transfer-Encoding: 8bit\n"
 "X-Poedit-Language: Catalan\n"
-"Plural-Forms: n != 1\n"
+"Plural-Forms: nplurals=2; plural=(n != 1);\n"
 
 #: ocitysmap/street_index.py:282
 msgid "Places of worship"