Correct mention of the tls-native-tls in the documentation.

[denschub]

The feature is called tls-native-tls, not tls-native:

sqlx/Cargo.toml

Line 77 in 258eaca

tls-native-tls = ["sqlx-core/_tls-native-tls", "sqlx-macros?/_tls-native-tls"]

So all the existing documentation is wrong.

I'd personally probably prefer tls-native as a feature name, but I wasn't sure if it's a good move to just change the name of that feature, so I decided to PR the docs change first. :)

[abonander]

Yeah I vacillated on what to call the feature, but decided to make it the same as the crate name it uses, for consistency.