Avoid vergen 2.1, it stops compiling in git worktrees

RalfJung · RalfJung · commit b6c07e98aae0 · 2018-10-08T10:22:02.000+02:00
diff --git a/Cargo.toml b/Cargo.toml
@@ -32,7 +32,7 @@ env_logger = "0.5"
 log = "0.4"
 
 [build-dependencies]
-vergen = "2"
+vergen = ">=2, <2.1"
 
 [features]
 cargo_miri = ["cargo_metadata"]
