Update apm to 2.6.2

1.58.0-beta0

1.57.0-beta0

1.56.0

Clang 9 is already in the image. (atom#22000)

It's on the PATH and is the version that will be used without needing to do update-alternatives.

1.56.0-beta0

Update the macOS Azure CI image to macos-10.15 (atom#21318)

Add authorization

1.54.0-beta0

1.53.0