use traditional HEREDOC delimiter

config.xhgui.yaml

@@ -2,20 +2,20 @@
 hooks:
   post-start:
   - exec: |
-      cat <<-PHP > .ddev/xhprof/xhprof_prepend.php
+      cat <<-EOF > .ddev/xhprof/xhprof_prepend.php
       <?php
       // DDEV's built in xhprof handler breaks our own.
       // We'll temporarily override it here, but return control back later.
       // If you don't want this behavior, comment out the hooks in ".ddev/config.xhgui.yaml".
       return;
-      PHP
+      EOF
   pre-stop:
   - exec: |
-      cat <<-PHP > .ddev/xhprof/xhprof_prepend.php
+      cat <<-EOF > .ddev/xhprof/xhprof_prepend.php
       <?php
       // #ddev-generated
       // We'll give back control of this file to DDEV. Next time it checks, it will see it has ownership
       // and override this file with the current default.
       // If you don't want this behavior, comment out the hooks in .ddev/config.xhgui.yaml.
       return;
-      PHP
+      EOF