Bump version for development (#62)

diff --git a/pyproject.toml b/pyproject.toml
index 2395ca3..807f358 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@
 
 [project]
 name        = "mypy_extensions"
-version     = "1.1.0-dev"
+version     = "1.2.0-dev"
 description = "Type system extensions for programs checked with the mypy type checker."
 readme      = "README.md"
 authors     = [