Support for Scala 2.13

[mgibowski]

It would be good to have a version for Scala 2.13.

I prepared a branch to support this version: master...mgibowski:scala-2.13

Here are necessary changes:

• replace usage of scala.collection.JavaConverters with scala.jdk.CollectionConverters,
• update dependency on http4s, 0.20.15 -> 0.21.0-M6.

My branch is not ready for a PR, the cross compilation is not fully set up. To be able to publish artifacts locally, I first need to publish them with the setting scalaVersion := scala212 and then again with the setting scalaVersion := scala213 and each time they get only published with the current scala version. I don't have much time now to fix it, but maybe the above info is useful for you.

[hanny24]

I don't think we want to update http4s dependency as we would like to stay on a "stable" version if possible. However, I think we could exclude http4s module from cross compilation.

[tomasherman]

I agree with hanny - is http4s module for 2.13 important for you?

[mgibowski]

I agree with hanny - is http4s module for 2.13 important for you?

Yes, currently I use it together with http4s.

[tomasherman]

i think we can use something like this, then:

https://github.com/scala/scala-module-dependency-sample

[tomasherman]

@mgibowski #103 what do you think

[tomasherman]

please try version 0.4.0 it should be xcompiled with proper http4s version