Change Run Chromium section in mac_build_instructions.md

Bug: 
Change-Id: I0e7d08124fa62d3da99b76783de21c9dce06dcc4
Reviewed-on: https://chromium-review.googlesource.com/552904
Reviewed-by: Sidney San Martin <[email protected]>
Commit-Queue: Owen Min <[email protected]>
Cr-Commit-Position: refs/heads/master@{#483144}
diff --git a/docs/mac_build_instructions.md b/docs/mac_build_instructions.md
index 1a9824a6..c3a9234 100644
--- a/docs/mac_build_instructions.md
+++ b/docs/mac_build_instructions.md
@@ -152,7 +152,7 @@
 Once it is built, you can simply run the browser:
 
 ```shell
-$ out/Default/chrome
+$ out/Default/Chromium.app/Contents/MacOS/Chromium
 ```
 
 ## Running test targets