Fix artifactId of bindings on bintray

Currently artifactId in documentation does not match real one.

For example artifactId for [POSIX bindings](https://bintray.com/scala-native-bindgen/maven/libposix) is `libposix_native0.3` but [docs](https://scala-native.github.io/scala-native-bindgen/bindings/posix.html) say it's `libposix`.
I suppose we should change artifactId on bintray so it doesn't contain version and `_native` postfix.