bump version to v2.1.0

Author: zonyitoo

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "context"
-version = "2.0.1"
+version = "2.1.0"
 authors = ["Y. T. Chung <zonyitoo@gmail.com>", "Leonard Hecker <leonard@hecker.io>"]
 license = "MIT/Apache-2.0"
 repository = "https://github.com/zonyitoo/context-rs"