Use lowercase sha in docs

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

@@ -11,7 +11,7 @@ An alternative is to use this script which only works with UNIX utilities:
 
 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