Fix typo OnBefore -> NotBefore (node-saml#611)

Author: bcoughlan

README.md

@@ -127,7 +127,7 @@ type Profile = {
 - `additionalAuthorizeParams`: dictionary of additional query params to add to 'authorize' requests
 - `identifierFormat`: optional name identifier format to request from identity provider (default: `urn:oasis:names:tc:SAML:1.1:nameid-format:emailAddress`)
 - `wantAssertionsSigned`: if truthy, add `WantAssertionsSigned="true"` to the metadata, to specify that the IdP should always sign the assertions.
-- `acceptedClockSkewMs`: Time in milliseconds of skew that is acceptable between client and server when checking `OnBefore` and `NotOnOrAfter` assertion condition validity timestamps. Setting to `-1` will disable checking these conditions entirely. Default is `0`.
+- `acceptedClockSkewMs`: Time in milliseconds of skew that is acceptable between client and server when checking `NotBefore` and `NotOnOrAfter` assertion condition validity timestamps. Setting to `-1` will disable checking these conditions entirely. Default is `0`.
 - `maxAssertionAgeMs`: Amount of time after which the framework should consider an assertion expired. If the limit imposed by this variable is stricter than the limit imposed by `NotOnOrAfter`, this limit will be used when determining if an assertion is expired.
 - `attributeConsumingServiceIndex`: optional `AttributeConsumingServiceIndex` attribute to add to AuthnRequest to instruct the IDP which attribute set to attach to the response ([link](http://blog.aniljohn.com/2014/01/data-minimization-front-channel-saml-attribute-requests.html))
 - `disableRequestedAuthnContext`: if truthy, do not request a specific authentication context. This is [known to help when authenticating against Active Directory](https://github.com/node-saml/passport-saml/issues/226) (AD FS) servers.