modules/saml/docs/sp.txt: minor fix: ext[] -> $ext[].
modules/saml/docs/sp.txt: minor fix: ext[] -> $ext[].

simplesamlphp/saml2,ArtemTeleshev/php-saml2,sitya/saml2,newmen/saml2,madmatt/saml2,sgomez/saml2,cb8/saml2