Add cache busting of dashboard's custom script

[grayside]

The build.js file referenced by the main HTML markup of the dashboard contains all the content and custom styling for the dashboard as a Vue.js app. For lack of cache busting, when there are updates to the dashboard it requires extra cache clearing on the part of viewers.

Add some element of cache busting (querystring or otherwise) so new releases more smoothly deliver changes to users.

Since this is only a single file we'd prefer to minimize tooling additions to make this happen. (We do have webpack)