DOC: restore note about "independant" typo

The independant -> independent error was fixed in 801a0a35 ("DOC: fix
name for "option independant-streams"), but the note about the wrong
name was erroneously fixed in 0e82b92a ("DOC: fix a few config typos").

Restore the "wrong" name so that when reasearching this option people
can actually find it.

Could be backported to 1.8.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 2e6062c..9ce88bc 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -6281,7 +6281,7 @@
   data sent to the server. Doing so will typically break large HTTP posts from
   slow lines, so use it with caution.
 
-  Note: older versions used to call this setting "option independent-streams"
+  Note: older versions used to call this setting "option independant-streams"
         with a spelling mistake. This spelling is still supported but
         deprecated.