Gfortran dissappeared from build

I got this job from successful build https://travis-ci.org/ctlab/phantasus/jobs/452899717
And this job from failed build https://travis-ci.org/ctlab/phantasus/jobs/454405098
They are building the same commit, so i assume that the problem is not in the repo.
The reason of failing build is

/usr/bin/ld: cannot find -lgfortran

gfortran used to be installing by default and now it disappeared.
Not sure if it a bug. Should i add gfortran to travis configuration explicitly now?
cc @jeroen and @jimhester

I think it should be enabled by default but try setting fortran: true just in case.

Seems like a duplicate of R docker failing to download el-capitan.dmg - Environments / macOS - Travis CI Community

EDIT: this is for Linux but the reason is the same.