Make Contact page’s Calendly async

As the Calendly widget on my contact page is above-the-fold, `defer`ring
it is a little too aggressive, especially as it being in-`body` means
that it’s queued behind SpeedCurve etc. Switching to `async` keeps it
off the Critical Path but it’ll hopefully run a little sooner.

Body (72 chars)

Author: csswizardry

contact.md

@@ -15,10 +15,8 @@ Or book a free call:
 
 <noscript><a href="https://calendly.com/csswizardry/30min" class="btn  btn--full">Book a Free Call</a></noscript>
 
-<!-- Calendly inline widget begin -->
 <div class="calendly-inline-widget" data-url="https://calendly.com/csswizardry/30min?background_color=f9f9f9&text_color=333333&primary_color=f43059" style="min-width:320px;height:700px;margin-bottom:1.5rem;"></div>
-<script type="text/javascript" src="https://assets.calendly.com/assets/external/widget.js" defer fetchpriority=high></script>
-<!-- Calendly inline widget end -->
+<script src="https://assets.calendly.com/assets/external/widget.js" async fetchpriority=high></script>
 
 - - -