ITK nightly version update

This commit updates:
  (1) SHA used in CMakeLists.txt to checkout ITK sources
          (InsightSoftwareConsortium/ITK@967c14c)
  (2) VERSION variable set in itkVersion.py

It was automatically generated by the script update_python_version.sh [1]

[1] https://github.com/InsightSoftwareConsortium/ITKPythonPackage/blob/c0f12d7/scripts/update_python_version.py

Merge pull request InsightSoftwareConsortium#47 from thewtex/install-…

…command

doc: update install command