Update MangaElt.js

This should fix merges https://github.com/AllMangasReader-dev/AMR/issues/111
Trying to parse an array, that is already been parsed and instatntiated as an array is gonna blow up.

Test case:{\"mirror\":\"Manga-Fox\",\"name\":\"1/2 Prince\",\"url\":\"http://mangafox.me/manga/1_2_prince/\",\"lastChapterReadURL\":\"http://mangafox.me/manga/1_2_prince/v14/c069/\",\"lastChapterReadName\":\"1/2 Prince 69\",\"read\":0,\"update\":1,\"ts\":1407828322,\"display\":0,\"cats\":\"[]\"},