[docs] Fix path to run JUnit tests.

Change-Id: I1d42c3746af3cc76448f3d8b89a39f76dae527ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2247881
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Andrew Walbran <qwandor@google.com>
Cr-Commit-Position: refs/heads/master@{#780626}

docs/testing/android_test_instructions.md

@@ -172,10 +172,10 @@ For example, adding a test to `chrome_junit_tests` requires to update
 ninja -C out/Default chrome_junit_tests
 
 # Run the test suite.
-out/Default/run_chrome_junit_tests
+out/Default/bin/run_chrome_junit_tests
 
 # Run a subset of tests. You might need to pass the package name for some tests.
-out/Default/run_chrome_junit_tests -f "org.chromium.chrome.browser.media.*"
+out/Default/bin/run_chrome_junit_tests -f "org.chromium.chrome.browser.media.*"
 ```
 
 ### Debugging