Translate "OEBPS" filenames

We're expecting inzipinfo.filename == "OPS/content.opf" while this
value is "OEBPS/content.opf" for an EPUB file created with
LibreOffice.

#1

argostranslatefiles/formats/epub.py

@@ -24,7 +24,8 @@ def translate(self, underlying_translation: ITranslation, file_path: str):
 
         for inzipinfo in inzip.infolist():
             with inzip.open(inzipinfo) as infile:
-                if inzipinfo.filename == "OPS/content.opf" or inzipinfo.filename == "OPS/toc.ncx":
+                translatable_xml_filenames = ["OPS/content.opf", "OPS/toc.ncx", "OEBPS/content.opf", "OEBPS/toc.ncx"]
+                if inzipinfo.filename in translatable_xml_filenames:
                     soup = BeautifulSoup(infile.read(), 'xml')
 
                     itag = self.itag_of_soup(soup)