minor fixes in static html pages.

html/50x.html

@@ -18,7 +18,7 @@
 Please try again later.</p>
 <p>If you are the system administrator of this resource then you should check
 the <a href="http://nginx.org/r/error_log">error log</a> for details.</p>
-<p>We have articles on troubleshooting issues like <a href="https://blog.openresty.com/en/lua-cpu-flame-graph/?src=wb">high CPU usage</a>,
+<p>We have articles on troubleshooting issues like <a href="https://blog.openresty.com/en/lua-cpu-flame-graph/?src=wb">high CPU usage</a> and
 <a href="https://blog.openresty.com/en/how-or-alloc-mem/">large memory usage</a> on <a href="https://blog.openresty.com/">our official blog site</a>.
 <p><em>Faithfully yours, <a href="https://openresty.org/">OpenResty</a>.</em></p>
 </body>

html/index.html

@@ -21,7 +21,7 @@ working. Further configuration is required.</p>
 <a href="https://openresty.org/">openresty.org</a> site<br/>
 Commercial support is available at
 <a href="https://openresty.com/">openresty.com</a>.</p>
-<p>We have articles on troubleshooting issues like <a href="https://blog.openresty.com/en/lua-cpu-flame-graph/?src=wb">high CPU usage</a>,
+<p>We have articles on troubleshooting issues like <a href="https://blog.openresty.com/en/lua-cpu-flame-graph/?src=wb">high CPU usage</a> and
 <a href="https://blog.openresty.com/en/how-or-alloc-mem/">large memory usage</a> on <a href="https://blog.openresty.com/">our official blog site</a>.
 <p><em>Thank you for flying <a href="https://openresty.org/">OpenResty</a>.</em></p>
 </body>