Update conditions tag

Some of the service providers require "NotBefore" and "NotOnOrAfter" attributes in the <Conditions/> tag.

We were trying to configure `dustin-decker/saml-proxy` to work with `mujina-idp`, but came across security related exceptions
which we fixed locally by adding the formentioned attributes.

mujina-common/src/main/java/mujina/saml/SAMLBuilder.java

@@ -103,6 +103,8 @@ public static Assertion buildAssertion(SAMLPrincipal principal, Status status, S
     audienceRestriction.getAudiences().add(audience);
 
     Conditions conditions = buildSAMLObject(Conditions.class, Conditions.DEFAULT_ELEMENT_NAME);
+    conditions.setNotBefore(new DateTime().minusMinutes(3));
+    conditions.setNotOnOrAfter(new DateTime().plusMinutes(3));
     conditions.getAudienceRestrictions().add(audienceRestriction);
     assertion.setConditions(conditions);