Raise cxx-build's dev dependency on cxx-gen
diff --git a/gen/build/Cargo.toml b/gen/build/Cargo.toml
index 05cdc08..cfc1b5e 100644
--- a/gen/build/Cargo.toml
+++ b/gen/build/Cargo.toml
@@ -18,7 +18,7 @@
 syn = { version = "1.0.20", default-features = false, features = ["parsing", "printing", "clone-impls", "full"] }
 
 [dev-dependencies]
-cxx-gen = { version = "=0.0.1", path = "../lib" }
+cxx-gen = { version = "0.4", path = "../lib" }
 
 [package.metadata.docs.rs]
 targets = ["x86_64-unknown-linux-gnu"]