Fix typo, 'Mostar Salas' to 'Mostrar Salas' (#1036)

locale/pt_BR/LC_MESSAGES/converse.po

@@ -929,7 +929,7 @@ msgstr "Entrar na sala"
 
 #: dist/converse-no-dependencies.js:21104
 msgid "Show rooms"
-msgstr "Mostar salas"
+msgstr "Mostrar salas"
 
 #: dist/converse-no-dependencies.js:21165
 msgid "Rooms"

locale/pt_BR/LC_MESSAGES/pt_BR.js

@@ -333,7 +333,7 @@
                 ],
                 "Show rooms": [
                     null,
-                    "Mostar salas"
+                    "Mostrar salas"
                 ],
                 "No rooms on %1$s": [
                     null,