Use clang-format version 10

[mcharleb]

We can see formatting differences between different versions of clang-format. Update CI to use version10 (Ubuntu 18.04 default version).

[bellycat77]

@mcharleb @relja128 Why should we use clang-format version 10?
We have no mentions of it in our README. Also, we have no mentions of Ubuntu 18.04.
Users can have Debian as the host system, for example. Or even MacOS. clang-format is a part of the host system in our case...

[bellycat77]

The default version of clang-format used in Ubuntu is 6.0. I mean Ubuntu in Docker-image, but version 10 is available too (as separate package)

[bellycat77]

So in our case, we could try to use clang-format from our Docker image (we need to modify the docker image and add the required version of clang-format )