Fix creation of json for image (pandoc 1.12.3.3)
Fix creation of json for image (pandoc 1.12.3.3)

At least with pandoc 1.12.3.3 otherwise you get an error

    pandoc: when expecting a [a], encountered Object instead
infotroph/pandocfilters,jgm/pandocfilters,timtylin/scholdoc-filters,silvio/pandocfilters,AugustH/pandocfilters,alycosta/pandocfilters