fix typo

Author: rouilj

doc/installation.txt

@@ -1140,7 +1140,7 @@ The Hiawatha and lighttpd web servers can run Roundup using FastCGI.
 Cherokee can run FastCGI but it also supports wsgi directly using a
 uWSGI, Gnuicorn etc.
 
-To run Roundup suing FastCGI, the flup_ package can be used under
+To run Roundup using FastCGI, the flup_ package can be used under
 Python 2 and Python 3. We don't have a detailed config for this, but
 the basic idea can be found at:
 https://flask.palletsprojects.com/en/2.0.x/deploying/fastcgi/