Bionic doesn't seem to be using a correct safelist

[native-api]

Reported at Cannot install git-svn apt-package - #11 by nijel

@nijel

I ran into this issue as well, but git-core seems to be not available via addon on Bionic based builds as it fails with Disallowing sources: git-core. So I had to specify the source manually there:

addons:
  apt:
    sources:
    - sourceline: ppa:git-core/ppa
    packages:
    - git-svn

While git-core is present as an alias at https://github.com/travis-ci/apt-source-safelist/blob/master/ubuntu.json#L199