Add a test file that checks the version

This new test establishes pytest_localserver.VERSION as part of the API
of the package. The test won't catch changes where that constant is
replaced by some other string value, but hopefully that's not a concern.

Author: diazona

tests/test_version.py

@@ -0,0 +1,6 @@
+import pytest_localserver
+
+
+def test_version():
+    assert hasattr(pytest_localserver, "VERSION")
+    assert isinstance(pytest_localserver.VERSION, str)