Use ISO 8601 format for date-time string in updated node
Use ISO 8601 format for date-time string in updated node

fixes #120

citation-style-language/csl-editor,citation-style-editor/csl-editor,citation-style-language/csl-editor,adam3smith/csl-editor,citation-style-editor/csl-editor,adam3smith/csl-editor,adam3smith/csl-editor,fbennett/csl-editor,fbennett/csl-editor,citation-style-editor/csl-editor,citation-style-language/csl-editor