Fix syntax error in french translation

[cfi-gb]

Build of the translations will currently fail with the following error:

Traceback (most recent call last):
  File "/usr/src/gsa-7.0.3/tools/po2json", line 66, in <module>
    main()
  File "/usr/src/gsa-7.0.3/tools/po2json", line 62, in main
    convert(sys.argv[1], sys.argv[2])
  File "/usr/src/gsa-7.0.3/tools/po2json", line 45, in convert
    po_f = polib.pofile(in_name)
  File "/usr/lib/python2.7/dist-packages/polib.py", line 138, in pofile
    return _pofile_or_mofile(pofile, 'pofile', **kwargs)
  File "/usr/lib/python2.7/dist-packages/polib.py", line 86, in _pofile_or_mofile
    instance = parser.parse()
  File "/usr/lib/python2.7/dist-packages/polib.py", line 1320, in parse
    self.process(keywords[tokens[0]])
  File "/usr/lib/python2.7/dist-packages/polib.py", line 1464, in process
    self.current_line)
IOError: Syntax error in po file (line 430)
src/po/CMakeFiles/gettext-json.dir/build.make:74: recipe for target 'src/po/gsad-fr.json' failed
make[2]: *** [src/po/gsad-fr.json] Error 1
CMakeFiles/Makefile2:1020: recipe for target 'src/po/CMakeFiles/gettext-json.dir/all' failed
make[1]: *** [src/po/CMakeFiles/gettext-json.dir/all] Error 2
Makefile:149: recipe for target 'all' failed
make: *** [all] Error 2

[cfi-gb]

Ref to a previous successful #471 and the related PR #393

CircleCI build in https://circleci.com/gh/greenbone/gsa/2096 probably succeeded because of some missing but optional dependencies:

-- Could NOT find Gettext (missing:  GETTEXT_MSGMERGE_EXECUTABLE GETTEXT_MSGFMT_EXECUTABLE) 
-- Found PythonInterp: /usr/bin/python (found version "2.7.9") 
-- Could NOT find PY_polib (missing:  PY_POLIB) 
CMake Warning at src/po/CMakeLists.txt:164 (message):
  Could not build translation files: gettext not found.