cmake UPDATE cmake version to 3.5 & fix var name
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0437dff..6bbc53f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 2.8.12)
+cmake_minimum_required(VERSION 3.5)
 
 project(libnetconf2 C)