CONTRIBUTORS: add Paul Murphy (IBM corporate CLA)

Change-Id: I9fecc76f8cbda364b467eab7b2e7381b963df892
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/255137
Trust: Ian Lance Taylor <iant@golang.org>
Trust: Than McIntosh <thanm@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
diff --git a/CONTRIBUTORS b/CONTRIBUTORS
index e4aa2d9..e151d46 100644
--- a/CONTRIBUTORS
+++ b/CONTRIBUTORS
@@ -58,6 +58,7 @@
 Matthieu Sarter <matthieu.sarter.external@atos.net>
 Michael Hudson-Doyle <michael.hudson@linaro.org>
 Nikhil Benesch <nikhil.benesch@gmail.com>
+Paul Murphy <murp@ibm.com>
 Peter Collingbourne <pcc@google.com>
 Rainer Orth <ro@cebitec.uni-bielefeld.de>
 Rémy Oudompheng <oudomphe@phare.normalesup.org> <remyoudompheng@gmail.com>