Mixed Content – https/http

Hello,
After updating to latest release I get a mixed content error:

Mixed Content: The page at ‘https://…../’ was loaded over HTTPS, but requested an insecure XMLHttpRequest endpoint ‘http://coincap.io/history/1day/BTC’. This request has been blocked; the content must be served over HTTPS.

What file should I edit to get this fixed?
Need to change to
https://coincap.io/history/1day/BTC