clang-tidy on variable name

[ordy]

Made a PR recently and clang-tidy threw some warnings related to variable naming style.

Apparently the project is following the Google's style guide, but the clang-tidy rule for variable names is set to camelBack and not lower_case.

So should someone change the clang-tidy rule to follow the style guide, or should we use camelBack for variable names now?