ENH: Bump ITK version to 4.12.0.

Change-Id: Ied65881442a2a7b286752edabdbeabbeee8faeb4

Author: Francois Budin

SuperBuild/External_ITKv4.cmake

@@ -103,8 +103,8 @@ if(NOT ( DEFINED "${extProjName}_DIR" OR ( DEFINED "USE_SYSTEM_${extProjName}" A
     )
   ### --- End Project specific additions
   set(${proj}_REPOSITORY ${git_protocol}://itk.org/ITK.git)
-  # ITK master 2017-01-24
-  set(${proj}_GIT_TAG "v4.11.0")
+  # ITK master 2017-06-01
+  set(${proj}_GIT_TAG "v4.12.0")
 
   ExternalProject_Add(${proj}
     GIT_REPOSITORY ${${proj}_REPOSITORY}