ITK nightly version update

This commit updates:
  (1) SHA used in CMakeLists.txt to checkout ITK sources
          (InsightSoftwareConsortium/ITK@90630cf)
  (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/dbef6cc/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 2018-03-30
-  set(ITK_GIT_TAG "1f6c5d2")
+  # ITK nightly-master 2018-03-31
+  set(ITK_GIT_TAG "90630cf")
 
   #-----------------------------------------------------------------------------
   # A separate project is used to download ITK, so that it can reused

itkVersion.py

@@ -1,4 +1,4 @@
-VERSION = '4.13.0.dev20180330+582.g1f6c5d2'
+VERSION = '4.13.0.dev20180331+584.g90630cf'
 
 def get_versions():
     """Returns versions for the ITK Python package.