Use alternative ABNF syntax so that things line up

Author: joker314

draft-foudil-securitytxt.md

@@ -422,7 +422,7 @@ sign-header      = <headers and line from section 7 of [RFC4880]>
 sign-footer      = <OpenPGP signature from section 7 of [RFC4880]>
 
 unsigned         = *line [canonical-field eol *line] [lang-field eol] *line
-unsigned         =/ *line [lang-field eol *line] [canonical-field eol] *line
+unsigned         / *line [lang-field eol *line] [canonical-field eol] *line
 
 line             = (field / comment) eol