contributors.sh: use "on github", not at

scripts/contributors.sh

@@ -6,7 +6,7 @@
 #                            | (__| |_| |  _ <| |___
 #                             \___|\___/|_| \_\_____|
 #
-# Copyright (C) 2013-2017, Daniel Stenberg, <daniel@haxx.se>, et al.
+# Copyright (C) 2013-2018, Daniel Stenberg, <daniel@haxx.se>, et al.
 #
 # This software is licensed as described in the file COPYING, which
 # you should have received as part of this distribution. The terms
@@ -50,6 +50,7 @@ cut -d: -f2- | \
 cut '-d(' -f1 | \
 cut '-d<' -f1 | \
 tr , '\012' | \
+sed 's/ at github/ on github/' | \
 sed 's/ and /\n/' | \
 sed -e 's/^ //' -e 's/ $//g' -e 's/@users.noreply.github.com$/ on github/'