tools/mb: Add Linux Goma RBE Prod builder to config

BUG=913249

Change-Id: Icacda434b78bc09b85290734f888f914dc91d3ac
Reviewed-on: https://chromium-review.googlesource.com/c/1369547Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Simon Que <sque@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615452}

tools/mb/mb_config.pyl

@@ -299,6 +299,7 @@
       'Chromium Mac Goma RBE Staging': 'release_bot',
       'Chromium Mac Goma RBE Staging (dbg)': 'debug_bot',
       'Chromium Android ARM 32-bit Goma RBE Staging': 'android_release_bot_minimal_symbols',
+      'Chromium Linux Goma RBE Prod': 'release_bot',
     },
 
     'chromium.gpu': {