add 'security:passport-saml:cert' to mandatory items

src/server/service/passport.js

@@ -60,6 +60,7 @@ class PassportService {
     this.mandatoryConfigKeysForSaml = [
       'security:passport-saml:isEnabled',
       'security:passport-saml:entryPoint',
+      'security:passport-saml:cert',
       'security:passport-saml:issuer',
       'security:passport-saml:attrMapId',
       'security:passport-saml:attrMapUsername',