site.conf.sample: fix reference to oe-git-proxy script

The name of the script is oe-git-proxy, not oe-git-proxy.sh.

(From meta-yocto rev: c10150d94e8830c82937f6b229672c194ef270bf)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-poky/conf/site.conf.sample

@@ -17,7 +17,7 @@ SCONF_VERSION = "1"
 #
 
 # To use git with a proxy, you must use an external git proxy command, such as
-# the one provided by scripts/oe-git-proxy.sh. To use this script, copy it to
+# the one provided by scripts/oe-git-proxy. To use this script, copy it to
 # your PATH and uncomment the following:
 #GIT_PROXY_COMMAND ?= "oe-git-proxy"
 #ALL_PROXY ?= "socks://socks.example.com:1080"