DOC: Fix ordered list in summary

Section 6 about the cache was placed between 7 and 8. This should
be backported to 2.1.

Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 432c265..7cf43d4 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -64,6 +64,12 @@
 5.3.1.      Global overview
 5.3.2.      The resolvers section
 
+6.    Cache
+6.1.      Limitation
+6.2.      Setup
+6.2.1.        Cache section
+6.2.2.        Proxy section
+
 7.    Using ACLs and fetching samples
 7.1.      ACL basics
 7.1.1.      Matching booleans
@@ -82,12 +88,6 @@
 7.3.6.        Fetching HTTP samples (Layer 7)
 7.4.      Pre-defined ACLs
 
-6.    Cache
-6.1.      Limitation
-6.2.      Setup
-6.2.1.        Cache section
-6.2.2.        Proxy section
-
 8.    Logging
 8.1.      Log levels
 8.2.      Log formats