update depependency to `~> 0.2.1`?

[Yuki-Inoue]

Current latest release of Daru is 0.2.1.

This gem, however, specifies dependency as ~> 0.1.5, which forces the library user to stick with the old version.

Is it possible to update the Daru dependency to ~> 0.2.1, and publish it as 0.1.1?

[athityakumar]

Sure, feel free to send in a PR 👍