CONTRIBUTORS: add jba, shantuo and shadams

Change-Id: Id2c8fc350d84b977c58ce3ad6928c91b08c3bd2b
Reviewed-on: https://code-review.googlesource.com/7350
Reviewed-by: Dave Day <djd@golang.org>

CONTRIBUTORS

@@ -22,10 +22,13 @@ Filippo Valsorda <hi@filippo.io>
 Glenn Lewis <gmlewis@google.com>
 Ingo Oeser <nightlyone@googlemail.com>
 Johan Euphrosine <proppy@google.com>
+Jonathan Amsterdam <jba@google.com>
 Luna Duclos <luna.duclos@palmstonegames.com>
 Michael McGreevy <mcgreevy@golang.org>
 Omar Jarjur <ojarjur@google.com>
 Paweł Knap <pawelknap88@gmail.com>
 Péter Szilágyi <peterke@gmail.com>
+Sarah Adams <shadams@google.com>
 Toby Burress <kurin@google.com>
+Tuo Shan <shantuo@google.com>
 Tyler Treat <ttreat31@gmail.com>