fix bug with defaulted move in msvc 12.0

doc/html/boost_optional/tutorial/performance_considerations.html

@@ -82,7 +82,7 @@
         the size</a>
       </h5>
 <p>
-        For the purpose of the followin analysis, considering memory layouts, we
+        For the purpose of the following analysis, considering memory layouts, we
         can think of it as:
       </p>
 <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">&gt;</span>