FIX: small typo in an example using the "Referer" header

It was reported that an example was manipulating a "Referrer" header instead
of the known "Referer" one. Even if it's an example wich doesn't break things,
the typo can be fixed.

The fix should be backported in 1.4/1.5/1.6 branches.
(cherry picked from commit d1b0f7c3e0b7e64cedcc67e7088645277617edc5)
(cherry picked from commit b0e7a1cd8376656d182d274053784eaf68326c85)
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 3324653..d5cd8b3 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -2062,7 +2062,7 @@
   Example:
         capture request header Host len 15
         capture request header X-Forwarded-For len 15
-        capture request header Referrer len 15
+        capture request header Referer len 15
 
   See also : "capture cookie", "capture response header" as well as section 8
              about logging.