Supress waring about deprecated QSignalMapper

[LukasWoodtli]

Summary

Suppress warnings about using QSignalMapper which is deprecated in Qt5.

Details

Deprecation warnings are disabled in the Qt example project.

Motivation and Context

The example project doesn't build when the warnings are enabled.

How Has This Been Tested?

Travis builds with Qt 5 on macOS.

Types of changes

• Bug fix (non-breaking change which fixes an issue).

Checklist:

• It is my own work, its copyright is implicitly assigned to the project and no substantial part of it has been copied from other sources (including Stack Overflow). In rare occasions this is acceptable, like in CMake modules where the original copyright information should be kept.
• I'm using the same code standards as the existing code (indentation, spacing, variable naming, ...).
• I've added tests for my code.
• I have verified whether my change requires changes to the documentation
• My change either requires no documentation change or I've updated the documentation accordingly.
• My branch has been rebased to master, keeping only relevant commits.

[coveralls]

Coverage remained the same at 62.47% when pulling d4e3247 on LukasWoodtli:QSignalMapperFix into dd424c1 on cucumber:master.