ENH: Bump ITK ExternalProject version to 4.12.2

Change-Id: If1d0c5ce2df6132fb3d1bf1f1e7b2b1a7c826d2e

Author: thewtex

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 ${git_protocol}://itk.org/ITK.git)
-  # ITK master 2017-06-01
-  set(${proj}_GIT_TAG "v4.12.0")
+  # ITK release 2017-09-12
+  set(${proj}_GIT_TAG "v4.12.2")
 
   ExternalProject_Add(${proj}
     GIT_REPOSITORY ${${proj}_REPOSITORY}