test: fix typos in error messages

test/simple/test-dgram-multicast-multi-process.js

@@ -85,7 +85,7 @@ if (cluster.isMaster) {
                 }
               });
 
-              console.error('%d received %d matching messges.', worker.pid
+              console.error('%d received %d matching messages.', worker.pid
                     , count);
 
               assert.equal(count, messages.length

test/simple/test-dgram-multicast-setTTL.js

@@ -35,7 +35,7 @@ try {
     thrown = true;
 }
 
-assert(thrown, 'Setting an invalid mutlicast TTL should throw some error');
+assert(thrown, 'Setting an invalid multicast TTL should throw some error');
 
 //close the socket
-socket.close();
+socket.close();