fix: clang-tidy

[sleepdefic1t]

Summary

It appears Clang-Tidy hasn't been working for a while now.

https://github.com/ArkEcosystem/cpp-client/runs/244421081#step:6:1
https://github.com/ArkEcosystem/cpp-client/runs/242002683#step:7:1
https://circleci.com/gh/ArkEcosystem/cpp-client/1551

The current CMake file incorrectly expects Clang-tidy v.6 since #116.
Since Tidy is part of the Clang-5 workflow, this PR changes the CMake config to use v.5

It also removes a non-working -header-filter call.
The current behavior is identical to the default clang-tidy -header-filter default of .*.
Since it doesn't work as expected, there's no reason to have it.

Checklist

• Documentation (if necessary)
• Tests (if necessary)
• Ready to be merged

Additional Comments

Clang-Tidy tests may fail/take a long time because it is checking the entire CURL and GTest libraries and their tests.
This also happens without the header-filter option as seen here:

• https://github.com/sleepdefic1t/cpp-client/runs/250639039#step:6:1

A subsequent PR will address this issue.

[sleepdefic1t]

@faustbrian
That failure is expected.

This PR was just to get Tidy actually running at all.
I plan to address proper filtering in another PR, but can work on it here if you prefer.