ITK nightly version update

This commit updates:
  (1) SHA used in CMakeLists.txt to checkout ITK sources
          (InsightSoftwareConsortium/ITK@8237e6fa6f)
  (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/ef9636a/scripts/update_python_version.py

Author: kwrobot

CMakeLists.txt

@@ -73,8 +73,8 @@ if(ITKPythonPackage_SUPERBUILD)
   include(ExternalProject)
 
   set(ITK_REPOSITORY "https://github.com/InsightSoftwareConsortium/ITK.git")
-  # ITK nightly-master 2020-02-12
-  set(ITK_GIT_TAG "ad99ff401d")
+  # ITK nightly-master 2020-02-13
+  set(ITK_GIT_TAG "8237e6fa6f")
 
   #-----------------------------------------------------------------------------
   # A separate project is used to download ITK, so that it can reused

itkVersion.py

@@ -1,4 +1,4 @@
-VERSION = '5.1rc01.dev20200212+162.gad99ff401d'
+VERSION = '5.1rc01.dev20200213+174.g8237e6fa6f'
 
 def get_versions():
     """Returns versions for the ITK Python package.