MB-48347: Update CMAKE_MINIMUM_REQUIRED to 3.13

Change-Id: Idc9f68d03e4643bed1fa27231933ca45e70d11a0
Reviewed-on: http://review.couchbase.org/c/geocouch/+/160932
Well-Formed: Restriction Checker
Tested-by: Chris Hillery <[email protected]>
Reviewed-by: Abhijeeth Nuthan <[email protected]>

Author: ceejatec

CMakeLists.txt

@@ -1,6 +1,6 @@
 PROJECT (geocouch)
 
-CMAKE_MINIMUM_REQUIRED (VERSION 2.8)
+CMAKE_MINIMUM_REQUIRED (VERSION 3.13)
 
 IF(NOT CMAKE_MODULE_PATH)
   SET(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/../tlm/cmake/Modules")