notice how the link that is erroring begins with 'http' not 'https'. http is inherently 'insecure'.
'http://fonts.googleapis.com/css?family=Open+Sans:300italic,400italic,600italic,400,300,600'you should be able to add an 's' to http and that should fix things.
what google has to say:
Always use https:// URLs when loading resources on your page. Use the Content-Security-Policy-Report-Only header to monitor mixed content errors on your site. Use the upgrade-insecure-requests CSP directive to protect your visitors from insecure content.
learn more here