Fix folder location in BrowserTestBase docs

I'll look at this now.

Perfect! Thanks a ton!

I looked at if this is getting all the locations with some ag and greps like:

(in middle lines of block comments)

ag -Q "/Functional" core | grep ".*:.*:.*\* " | grep Tests
ag -Q "\Functional" core | grep ".*:.*:.*\* " | grep Tests

also checks if all the Functional namespace classes *are* in src with lower case src:

ag "Drupal\\\Tests\\\.*\\\Functional" core | grep namespace
ag "Drupal\\\Tests\\\.*\\\Functional" core | grep namespace | grep -v src
ag "Drupal\\\Tests\\\.*\\\Functional" core | grep namespace | grep -v tests

rtbc from me also.

Committed 43ac93d and pushed to 8.1.x and 8.2.x. Thanks!