update default urls to use cdnjs
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"
+VEGA_JS_URL = "https://cdnjs.cloudflare.com/ajax/libs/vega/2.6.5/vega.min.js"
+VEGALITE_JS_URL = "https://cdnjs.cloudflare.com/ajax/libs/vega-lite/1.3.1/vega-lite.min.js"
+VEGAEMBED_JS_URL = "https://cdnjs.cloudflare.com/ajax/libs/vega-embed/2.2.0/vega-embed.min.js"
