old_contents: D3_JS_URL = "https://d3js.org/d3.v3.min.js"
  VEGA_JS_URL = "https://vega.github.io/vega/releases/v2.6.5/vega.js"
  VEGALITE_JS_URL = "https://vega.github.io/vega-lite-1/vega-lite.js"
  VEGAEMBED_JS_URL = "https://vega.github.io/vega-editor/vendor/vega-embed.js"
  
new_contents: D3_JS_URL = "https://d3js.org/d3.v3.min.js"
  VEGA_JS_URL = "https://vega.github.io/vega/releases/v2.6.5/vega.js"
  VEGALITE_JS_URL = "https://vega.github.io/vega-lite-v1/vega-lite.js"
  VEGAEMBED_JS_URL = "https://vega.github.io/vega-editor/vendor/vega-embed.js"
  
subject: correct default url for version 1 of vega-lite.js