Remove error producing parts in README.md file

[harryadel]

Removed surrounding parentheses as they were preventing settings.json file from being properly read.

 "attributesSAML": [telephoneNumber, sn, givenName, mail], 

Also, modified the helper function to be a bit more concise and use a bit of ES6 features.

  'click .saml-login' (event) {
    event.preventDefault();
    let provider = event.target.getAttribute('data-provider');
    Meteor.loginWithSaml({
      provider
    }, function(error, result) {
      //handle errors and result
    });
  }