docs: Change single occurrence of "Micropython" to "MicroPython".

Author: dpgeorge

docs/topindex.html

@@ -48,7 +48,7 @@ <h1>MicroPython documentation</h1>
         {% endif %}
       </p>
       <p class="biglink">
-        <a class="biglink" href="{{ pathto("genrst/index") }}">Micropython Differences</a><br/>
+        <a class="biglink" href="{{ pathto("genrst/index") }}">MicroPython Differences</a><br/>
         <span class="linkdescr">MicroPython operations which differ from CPython</span>
       </p>
     </td>