Update help text for flag enable_strict_transport_security (#642)
Update help text for flag enable_strict_transport_security (#642)

* Update help text for flag enable_strict_transport_security

Signed-off-by: Wayne Zhang <bc786b8a4d6362cffdb954a38777b93c3461fd92@google.com>

* revert a test change

Signed-off-by: Wayne Zhang <bc786b8a4d6362cffdb954a38777b93c3461fd92@google.com>
GoogleCloudPlatform/esp-v2,GoogleCloudPlatform/esp-v2,GoogleCloudPlatform/esp-v2,GoogleCloudPlatform/esp-v2,GoogleCloudPlatform/esp-v2