increment patch version, as this is a bug fix.

Author: amoodie

pyDeltaRCM/_version.py

@@ -3,4 +3,4 @@ def __version__() -> str:
     Private version declaration, gets assigned to pyDeltaRCM.__version__
     during import
     """
-    return "2.1.7"
+    return "2.1.8"