Rename WebRTC Linux builder.

Missed mb_config.pyl in my previous CL.

Bug: 877018
Change-Id: I897caf43b76190a8e59e07e99436f5b5e48f1b07
Tbr: jbudorick@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/1337342Reviewed-by: Patrik Höglund <phoglund@chromium.org>
Commit-Queue: Patrik Höglund <phoglund@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608350}

tools/mb/mb_config.pyl

@@ -485,7 +485,7 @@
 
     'chromium.webrtc': {
       'Android Builder': 'android_debug_static_bot_arm64',
-      'Linux Builder': 'gpu_tests_release_bot',
+      'WebRTC Chromium Linux Builder': 'gpu_tests_release_bot',
       'Mac Builder': 'gpu_tests_release_bot',
       'Win Builder': 'release_bot_x86_minimal_symbols_no_com_init_hooks_with_codecs',
     },