pip install package from requirements fails, "uses insecure transport scheme"

Question

I'm trying to install django-forms-builder via an entry in the requirements.txt file. When running

pip install -r requirements.txt

I receive the error

django-forms-builder/0.11.1 uses an insecure transport scheme (http). Consider using https if  has it available
django-forms-builder/ uses an insecure transport scheme (http). Consider using https if  has it available
Could not find any downloads that satisfy the requirement django-forms-builder==0.11.1 (from -r requirements.txt (line 33))

The message is very clear, it wants https, but I need to install the package anyway. It works when I install it separately outside of the requirements file with a simple

pip install django-forms-builder

so how can I force the requirements to accept it as well?