Be consistent with usage of em-dashes in content files

[hnarayanan]

At the moment they're scattered between actually using the unicode character and --/---. e.g.

[content] grep -riI '—' ./*                                                                  10:12:44  ☁  master ☂ ✚ ✭
./projects/personal-website.md: <time class="post-date">date</time> — <time class="post-date">date</time>
./projects/personal-website.md: <time class="post-date">date</time> — <time class="post-date">date</time>
./projects/personal-website.md: <time class="post-date">date</time> — <time class="post-date">date</time>
./projects/personal-website.md: <time class="post-date">date</time> — <time class="post-date">date</time>
./projects/personal-website.md: <time class="post-date">2001</time> — <time class="post-date">2003</time>
./writing/kubernetes-django.md:4. Understanding Kubernetes from the ground up — [Kubelet][kubernetes-kubelet],
./writing/kubernetes-django.md:7. Deploying Django with Kubernetes — [Talk][kubernetes-django-talk],
./writing/kubernetes-django.md:Kubernetes — [Part 1][kubernetes-rails-1], [Part
./writing/lacking-functional-teats.md:volunteer baby-sitting their baby—especially if the
./writing/lacking-functional-teats.md:As you begin to change—after gingerly giving-in to lowering her for a
./writing/lacking-functional-teats.md:bit and keeping her in plain sight—whatever you do, put on another