PHP 7.2 stdout and stderr sentinels don't print in a new line

[csantanapr]

The user expects output to stdout and stderr to always show in logs.
Sentinels always print fine in 7.1, but not in 7.2
Take the following action example

<?php
function main(array $args) : array {
    echo 'hello stdout';
    file_put_contents("php://stderr",'hello stderr');
    return $args;
}

The test action purposely doesn't print a new line, but the sentinel should printed in a new line for the invoker to pick the output to logs correctly

• Run with the php 7.1 user container image

$ docker run -p 8080:8080 whisk/action-php-v7.1:latest
PHP 7.1.18 Development Server started at Mon Nov 12 21:10:55 2018
hello stderr
XXX_THE_END_OF_A_WHISK_ACTIVATION_XXX
hello stdout
XXX_THE_END_OF_A_WHISK_ACTIVATION_XXX

• Run with the php 7.2 user container image

$ docker run -p 8080:8080 whisk/action-php-v7.2:latest
PHP 7.2.6 Development Server started at Mon Nov 12 21:10:32 2018
hello stderrXXX_THE_END_OF_A_WHISK_ACTIVATION_XXX
hello stdoutXXX_THE_END_OF_A_WHISK_ACTIVATION_XXX