Update native-tls version to 0.2

[lunaryone]

No description provided.

[sfackler]

This doesn't appear to compile.

[lunaryone]

Build completed successfully with latest stable rustc 1.29
Tests are passed successfully

[est31]

The build failure is due to one of the dependencies having started to require >1.17 Rust. According to travis, compilation works on stable.

[est31]

One thing I'm not sure about though is the removal of the public method... it means that this PR constitutes a semver breaking change. Is there some way to avoid that?

[lunaryone]

The new implementation of TlsConnector (native-tls 2.1) has no method danger_connect_without_providing_domain_for_certificate_verification_and_server_name_indicatio

All configuration of the TlsConnector should be done in TlsConnectorBuilder.
I see no ways to avoid breaking changes
The old functionality is still accessible via custom TlsConnector and method from

[sfackler]

This upgrade is a breaking change no matter what the API surface looks like - native-tls is a public dependency of this crate.

[lunaryone]

@sfackler Could you please clarify what do you expect from my side?

[sfackler]

Let's bump the minimum supported Rust version to fix the build, and then I'll cut an 0.3 release.

[lunaryone]

The minimum supported version to build it is 1.21

[sfackler]

This should be good to go with a rebase.