Upgrade to latest testcontainers version

[natevecc]

The version of testcontainers this is using is behind by a few versions and I'd like to upgrade it to the most recent version. I'll try and do it on my own when I have some free time but any direction and guidance would be really appreciated.

[dimafeng]

@natevecc Sorry for not updating the version for a while. I'll be able to do it later today.

If you would like to help me with it, you can do the following:

1. Update the version of TestConteiners in https://github.com/testcontainers/testcontainers-scala/blob/master/gradle.properties
2. Run ./gradlew clean -Pscala=2.11.8 test integrationTest and ./gradlew clean -Pscala=2.12.1 test integrationTest
3. if it passes all the tests, I'll be able to release the new version today.

[natevecc]

Quick update: tests were initially failing because of this bug which is caused by this. However once I manually pulled the images needed by the tests, commented out the offending config file, then ran the tests everything passed. I'll put up a PR for this soon.

[dimafeng]

@natevecc thank you for your contribution. I'm going to release the new version soon.