serving/samples/helloworld-php: render newline (#1224)

* serving/samples/helloworld-php: render newline

* Double quotes in README too

docs/serving/samples/hello-world/helloworld-php/README.md

@@ -28,7 +28,7 @@ recreate the source files from this folder.
    ```php
    <?php
    $target = getenv('TARGET', true) ?: 'World';
-   echo sprintf('Hello %s!', $target);
+   echo sprintf("Hello %s!", $target);
    ```
 
 1. Create a file named `Dockerfile` and copy the code block below into it. See

docs/serving/samples/hello-world/helloworld-php/index.php

@@ -1,3 +1,3 @@
 <?php
 $target = getenv('TARGET', true) ?: 'World';
-echo sprintf('Hello %s!', $target);
+echo sprintf("Hello %s!", $target);