how-to-install-composer-programmatically.md: quotes are seatbelts

doc/faqs/how-to-install-composer-programmatically.md

@@ -9,9 +9,9 @@ An alternative is to use this script which only works with unix utils:
 ```bash
 #!/bin/sh
 
-EXPECTED_SIGNATURE=$(wget -q -O - https://composer.github.io/installer.sig)
+EXPECTED_SIGNATURE="$(wget -q -O - https://composer.github.io/installer.sig)"
 php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
-ACTUAL_SIGNATURE=$(php -r "echo hash_file('SHA384', 'composer-setup.php');")
+ACTUAL_SIGNATURE="$(php -r "echo hash_file('SHA384', 'composer-setup.php');")"
 
 if [ "$EXPECTED_SIGNATURE" != "$ACTUAL_SIGNATURE" ]
 then