COMP: fix CMake Deprecation Warning (Compatibility with CMake < 2.8.12)

This is just a convenience commit to get rid of the warnings for 5.2 final.
These libraries should be updated in a normal way once 5.3 development starts.

Text of the error messages:

CMake Deprecation Warning at Modules/ThirdParty/GoogleTest/src/itkgoogletest/CMakeLists.txt:4 (cmake_minimum_required):
  Compatibility with CMake < 2.8.12 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.

CMake Deprecation Warning at Modules/ThirdParty/GoogleTest/src/itkgoogletest/googletest/CMakeLists.txt:56 (cmake_minimum_required):
  Compatibility with CMake < 2.8.12 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.

CMake Deprecation Warning at Modules/ThirdParty/MINC/src/libminc/CMakeLists.txt:25 (CMAKE_MINIMUM_REQUIRED):
  Compatibility with CMake < 2.8.12 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.

Modules/ThirdParty/GoogleTest/src/itkgoogletest/CMakeLists.txt

@@ -1,7 +1,7 @@
 # Note: CMake support is community-based. The maintainers do not use CMake
 # internally.
 
-cmake_minimum_required(VERSION 2.8.8)
+cmake_minimum_required(VERSION 2.8.12)
 
 if (POLICY CMP0048)
   cmake_policy(SET CMP0048 NEW)

Modules/ThirdParty/GoogleTest/src/itkgoogletest/googletest/CMakeLists.txt

@@ -53,7 +53,7 @@ else()
   cmake_policy(SET CMP0048 NEW)
   project(gtest VERSION ${GOOGLETEST_VERSION} LANGUAGES CXX C)
 endif()
-cmake_minimum_required(VERSION 2.6.4)
+cmake_minimum_required(VERSION 2.8.12)
 
 if (POLICY CMP0063) # Visibility
   cmake_policy(SET CMP0063 NEW)

Modules/ThirdParty/MINC/src/libminc/CMakeLists.txt

@@ -22,7 +22,7 @@ INCLUDE(CTest)
 
 ENABLE_TESTING()
 
-CMAKE_MINIMUM_REQUIRED(VERSION 2.8)
+CMAKE_MINIMUM_REQUIRED(VERSION 2.8.12)
 
 IF( POLICY CMP0063 )
   CMAKE_POLICY(SET CMP0063 NEW)