BLD: Remove deprecated pip --use-mirrors flag.

With release 1.5 pip deprecated the --use-mirrors flag,
since that release the flag is a noop and raises a deprecation warning.

etc/ordered_pip.sh

@@ -4,7 +4,7 @@ a=0
 while read line
 do     
     if [[ -n "$line" && "$line" != \#* ]] ; then
-        pip install --use-mirrors $line
+        pip install $line
     fi
     ((a = a + 1))
 done < $1