added tests for utils.py at tests/test_utils.py also changed a keyword argument from headers to user_agent for latest_version of utils.py with the usual default vaule.

tests/test_utils.py

@@ -0,0 +1,13 @@
+from waybackpy.utils import latest_version, DEFAULT_USER_AGENT
+from waybackpy.__version__ import __version__
+
+
+def test_default_user_agent():
+    assert (
+        DEFAULT_USER_AGENT
+        == "waybackpy %s - https://github.com/akamhy/waybackpy" % __version__
+    )
+
+
+def test_latest_version():
+    assert __version__ == latest_version(package_name="waybackpy")