Bump prerelease version

sleap/version.py

@@ -10,4 +10,4 @@ For example, if you set the version to X.Y.Z, then the tag should be "vX.Y.Z".
 
 Must be a semver string, "aN" should be appended for alpha releases.
 """
-__version__ = "1.1.0a8"
+__version__ = "1.1.0a9"