Fix SpeedCurve unquoted attribute issue

It was fully functional, but a bit brittle. I should probably just stop
using unquoted values.

Author: csswizardry

demo/index.html

@@ -183,7 +183,7 @@
     LUX.label = 'Obs.js';
     //# sourceURL=speedcurve.inline.js
   </script>
-  <script src=https://cdn.speedcurve.com/js/lux.js?id=47684395 defer crossorigin></script>
+  <script src="https://cdn.speedcurve.com/js/lux.js?id=47684395" defer crossorigin></script>
 
   <script src="https://www.googletagmanager.com/gtag/js?id=G-DNCL1RY4GT" async crossorigin></script>
   <script>