Update minimum version of cmake

Signed-off-by: Travis Collins <travis.collins@analog.com>

Author: tfcollins

CMakeLists.txt

@@ -10,7 +10,7 @@
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 # Lesser General Public License for more details.
 
-cmake_minimum_required(VERSION 2.8.12)
+cmake_minimum_required(VERSION 3.5.0)
 project(ad9361 C)
 
 set(LIBAD9361_VERSION_MAJOR 0)