Cross build for scala 2.13.1

[utgheith]

updated dependencies to:
sbt 1.3.4
scala-async 0.10.0
play-ahc-ws 2.7.3
scalatest 3.0.8
cats-core 2.0.0
monix 3.1.0
sbt-scalajs 0.6.31
algebird-core 0.13.6
cats-testkit 2.0.0

The unsupported "return - only" test fails to compile with:

return statement uses an exception to pass control to the caller of the enclosing named method t

Fixes #issue_number

#9

Problem

Adding support for Scala 2.13

Solution

• Changed build.sbt to cross build for 2.12 and 2.13
• Moved dependencies to later releases with 2.13 support
• Fixed various new warnings and upgraded uses of deprecated APIs

Notes

The unsupported "return - only" test fails to compile with:

return statement uses an exception to pass control to the caller of the enclosing named method t

Checklist

• Unit test all changes
• Update README.md if applicable
• Add [WIP] to the pull request title if it's work in progress
• Squash commits that aren't meaningful changes
• Run sbt scalariformFormat test:scalariformFormat to make sure that the source files are formatted

[TimSoethout]

I hope we can get this merged. This is a blocker for me at the moment.

[dsilvasc]

@utgheith That build failure seems related to https://travis-ci.community/t/error-installing-oraclejdk8-expected-feature-release-number-in-range-of-9-to-14-but-got-8/3766/13

Might want to try one of the workarounds from that thread: either changing from oraclejdk8 to openjdk8 or specifying the ubuntu distribution (dist: trusty) in https://github.com/monadless/monadless/blob/master/.travis.yml

[dsilvasc]

trying to get past the build error #66