Fix apt-get command in dockerfile

4 jobs for 14-c-fortran-bindings in 2 minutes and 48 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #38198
manual
build_docker_base

00:02:22

 
  Test
passed #38199
build_test_cmake

00:00:17

passed #38201
test_lint

00:00:25

failed #38200
test_py3

00:00:11

 
Name Stage Failure
failed
test_py3 Test
$ tox -e py37 -- -sv
GLOB sdist-make: /builds/grp-svergun/galumph/setup.py
py37 create: /builds/grp-svergun/galumph/.tox/py37
ERROR: InterpreterNotFound: python3.7
___________________________________ summary ____________________________________
ERROR: py37: InterpreterNotFound: python3.7
Running after_script
Uploading artifacts for failed job
ERROR: Job failed: exit code 1