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)
1 file changed