fix placeholder
fix placeholder

previous implementation worked because setContents was triggering an
noop text change event

sferoze/quilljs,sferoze/quilljs,willrowe/quill,quilljs/quill,quilljs/quill,sferoze/quilljs,willrowe/quill,willrowe/quill,voxmedia/quill,voxmedia/quill,sferoze/quilljs,voxmedia/quill,quilljs/quill