Building the container on windows fails

[p3trus]

When trying to build the container on windows, the following error appears:

readthedocs_1    | 2018-11-02 11:45:33,675 INFO spawned: 'readthedocs-bootstrap' with pid 14
: invalid option | /bin/bash: -
readthedocs_1    | 2018-11-02 11:45:33,680 INFO exited: readthedocs-bootstrap (exit status 1; not expected)
readthedocs_1    | 2018-11-02 11:45:34,681 INFO gave up: readthedocs-bootstrap entered FATAL state, too many start retries too quickly

This is related to the fact that git checks out files with the native file ending (\r\n on windows). The invalid shell scripts are then copied to the linux container resulting in this error.