md4qt: bump version

[igormironchik]

Specify library name and version: md4qt/2.0.15

I'm the author of this library.

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• I've read the contributing guidelines.
• I've used a recent Conan client version close to the currently deployed.
• I've tried at least one configuration locally with the conan-center hook activated.

[conan-center-bot]

Conan v1 pipeline ✔️

All green in build 1 (19806e6c4e8a658a16cf04915539071152b67dd9):

• md4qt/2.0.15:
  All packages built successfully! (All logs)

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Conan v2 pipeline ✔️

Note: Conan v2 builds may be required once they are on the v2 ready list

All green in build 1 (19806e6c4e8a658a16cf04915539071152b67dd9):

• md4qt/2.0.15:
  All packages built successfully! (All logs)

[conan-center-bot]

This PR has been automatically merged due to Bump version or Bump dependencies label.
Read https:/conan-io/conan-center-index/blob/master/docs/labels.md#bump-version to obtain more information.