Use idiomatic dependencies in Cargo.toml

[matklad]

In Cargo, it's very very rare that one actually needs ^ or ~ deps in Cargo.toml. Default foo = "1.2.3" will do the right thing most of the time. In this particular case, all of ^1, ~1 and 1 would be equivalent, and there's no need to stray from default.

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[cla-checker-service[bot]]

❌ Author of the following commits did not sign a Contributor Agreement: acc7e8bcf653cda561613f5046ff8ebd41fb91f8

Please, read and sign the above mentioned agreement if you want to contribute to this project

[matklad]

Ok, signing docusign CLA is a bit more than I am ready to do this morning :) Still, I'd advise to fix the readme to promote idiomatic usage :-)