Change ARM default download to 64-bit

Change the default for ARM to the aarch64 download. 64-bit ARM is the
standard nowadays for the type of consumer computing hardware our users
tend to have (Raspberri pi's and servers). While 32-bit ARM is only still
used in low-power embedded systems.

Closes #1099.

Author: laanwj

_includes/templates/download.html

@@ -73,7 +73,7 @@ <h2>{{ page.latestversion }} {{CURRENT_RELEASE}} <a type="application/rss+xml" h
       <div>
         <img src="/assets/images/os/arm.png" alt="ARM Linux">
         <span>
-          <a href="{{ PATH_PREFIX }}/{{ FILE_PREFIX }}-arm-linux-gnueabihf.tar.gz" class="dl">ARM Linux</a>
+          <a href="{{ PATH_PREFIX }}/{{ FILE_PREFIX }}-aarch64-linux-gnu.tar.gz" class="dl">ARM Linux</a>
           	<span><a href="{{ PATH_PREFIX }}/{{ FILE_PREFIX }}-aarch64-linux-gnu.tar.gz" class="dl" id="lin64arm">64 bit</a> -
             	<a href="{{ PATH_PREFIX }}/{{ FILE_PREFIX }}-arm-linux-gnueabihf.tar.gz" class="dl" id="lin32arm">32 bit</a></span>
         </span>