DOC: fix discrepancy in the example for http-request redirect

Commit c8f0e78 ("DOC: typo: req.uri is now replaced by capture.req.uri")
fixed a discrepancy in the doc but the scheme is still missing, resulting
in a redirect loop. Let's fix this as well. This should be backported to
1.5.
(cherry picked from commit 596659b023b01d8a81ae262af9ccab5ea2cb313f)
(cherry picked from commit 9b697e6afbbe55e5f00b14d99a535199837a2d5a)
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 57a62da..26b1f0e 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -5505,8 +5505,9 @@
         redirect scheme https if !{ ssl_fc }
 
   Example: append 'www.' prefix in front of all hosts not having it
-        http-request redirect code 301 location \
-          www.%[hdr(host)]%[capture.req.uri] unless { hdr_beg(host) -i www }
+        http-request redirect code 301 location      \
+          http://www.%[hdr(host)]%[capture.req.uri]  \
+          unless { hdr_beg(host) -i www }
 
   See section 7 about ACL usage.