set development version to v2.9.1-pre

ranocha · ranocha · commit e1375a00ea6a · 2022-01-23T13:27:52.000+01:00
diff --git a/Project.toml b/Project.toml
@@ -1,7 +1,7 @@
 name = "RootedTrees"
 uuid = "47965b36-3f3e-11e9-0dcf-4570dfd42a8c"
 authors = ["Hendrik Ranocha <mail@ranocha.de> and contributors"]
-version = "2.9.0"
+version = "2.9.1-pre"
 
 [deps]
 Latexify = "23fbe1c1-3f47-55db-b15f-69d7ec21a316"
