Replace <br/> with <br>

This is an effort to have more consistent markup, also related to
ongoing work with adding local anchors to comments:
Danielovich/PloehComments#5

If anyone's wondering why I don't just make a search-and-replace, I want
to visually verify that these changes don't mess anything up - at least
for a few posts.

If you're a front-end developer and find this ridiculous, then please
have patience with me. I rarely deal with such issues these days, and I
haven't kept up with web page rendering or HTML standards.

_posts/2015-08-03-idiomatic-or-idiosyncratic.html

@@ -403,7 +403,7 @@ <h2 id="comments-header">
   <div class="comment" id="575e427b726540e3a2f94b7f5360a5fa">
     <div class="comment-author"><a href="https://github.com/oteku">Thomas</a></div>
     <div class="comment-content">
-      <p>To end the loop it may be fair to give a JavaScript function sample which became more idiomatic since 2015 :) <br/>
+      <p>To end the loop it may be fair to give a JavaScript function sample which became more idiomatic since 2015 :) <br>
         ES5 syntax to be consistent with the first example.
       </p>
         <pre>