Remove build_dir arg from xvfb.py

[email protected]
BUG=670470

Review-Url: https://codereview.chromium.org/2521353003
Cr-Commit-Position: refs/heads/master@{#436652}
diff --git a/docs/linux_debugging.md b/docs/linux_debugging.md
index 0049fd9d..3f53fc3 100644
--- a/docs/linux_debugging.md
+++ b/docs/linux_debugging.md
@@ -364,7 +364,7 @@
 
 Alternatively, you can use testing/xvfb.py to set up your environment for you:
 
-    testing/xvfb.py out/Debug out/Debug/browser_tests \
+    testing/xvfb.py out/Debug/browser_tests \
         --gtest_filter="MyBrowserTest.MyActivateWindowTest"
 
 ### BROWSER_WRAPPER