Fix Event default timestamp (#24)

Co-authored-by: calle <93376500+callebtc@users.noreply.github.com>

test/test_event.py

@@ -0,0 +1,9 @@
+from nostr.event import Event
+from nostr.key import PrivateKey
+import time
+
+def test_event_default_time():
+    time.sleep(1.5)
+    public_key = PrivateKey().public_key.hex()
+    event = Event(public_key=public_key, content='test event')
+    assert (event.created_at - time.time()) < 1