Upgrade pip before installing the server's dependencies

[ivanhrabcak]

This caused me a lot of problems when first setting up (it just didn't work), until I've upgraded pip before installing packages that depend on jsonschema. (jsonschema needs newer pip to build its dependencies)

The changes I am proposing fixed the issue for me.

[werzum]

I had the same problem with jsonschema and luckily had a look in the pull requests - can confirm that this fixes the issue.

[11223300a]

I had the same problem with jsonschema and luckily had a look in the pull requests - can confirm that this fixes the issue.

Thanks. I also had to upgrade pip AND setuptools to get it to install on my machine. I put both of these lines before the line COPY requirements.txt requirements.txt:

RUN pip install --upgrade pip RUN install --upgrade setuptools

[ivanhrabcak]

Thank you, I will add this to my PR later today.