build: increase minimum cmake version to 3.5

The original minimum CMake version 3.0 will cause the following CMake
warning:

CMake Deprecation Warning at CMakeLists.txt:31 (cmake_minimum_required):
  Compatibility with CMake < 3.5 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.

In order to fix this warning, we need to increase the minimum CMake
version to 3.5.

CMakeLists.txt

@@ -28,7 +28,7 @@
 # SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 ################################################################################
 
-cmake_minimum_required(VERSION 3.0)
+cmake_minimum_required(VERSION 3.5)
 
 set(ARGTABLE3_PROJECT_NAME "argtable3")
 set(ARGTABLE3_PACKAGE_NAME "Argtable3")