test: fix function name typo

It doesn't affect the semantics of the test because it checks if that
particular bit of code throws an exception. It does, only it's a SyntaxError.

test/simple/test-domain-timers.js

@@ -45,7 +45,7 @@ immediated.on('error', function(e) {
 });
 
 immediated.run(function() {
-  setImmedaite(function() {
+  setImmediate(function() {
     throw new Error('Immediate Error');
   });
 });