Add explicit https to the loading of google analytics, as Google now …

…suggests. Maybe fix the events not sent problem (#70)?

src/api/ga.js

@@ -11,7 +11,7 @@
     a.async = 1;
     a.src = g;
     m.parentNode.insertBefore(a, m);
-})(window, document, "script", "//www.google-analytics.com/analytics.js", "ga");
+})(window, document, "script", "https://www.google-analytics.com/analytics.js", "ga");
 
 let gaTrackingId = sizeme_options.gaTrackingId;