Swap out bootstrap CDN
Swap out bootstrap CDN

(the canonical one was suffering from a
NET::ERR_CERTIFICATE_TRANSPARENCY_REQUIRED in Chromium, at least)

ebmdatalab/openprescribing,annapowellsmith/openpresc,annapowellsmith/openpresc,annapowellsmith/openpresc,ebmdatalab/openprescribing,annapowellsmith/openpresc,ebmdatalab/openprescribing,ebmdatalab/openprescribing