[Yaml] added backtick to the list of characters that trigger quotes as it is reserved for future use (patch from indeyets)

src/Symfony/Components/Yaml/Inline.php

@@ -80,7 +80,7 @@ class Inline
         return is_infinite($value) ? str_ireplace('INF', '.Inf', strval($value)) : (is_string($value) ? "'$value'" : $value);
       case false !== strpos($value, "\n") || false !== strpos($value, "\r"):
         return sprintf('"%s"', str_replace(array('"', "\n", "\r"), array('\\"', '\n', '\r'), $value));
-      case preg_match('/[ \s \' " \: \{ \} \[ \] , & \* \#] | \A[ - ? | < > = ! % @ ]/x', $value):
+      case preg_match('/[ \s \' " \: \{ \} \[ \] , & \* \#] | \A[ - ? | < > = ! % @ ` ]/x', $value):
         return sprintf("'%s'", str_replace('\'', '\'\'', $value));
       case '' == $value:
         return "''";