Merge pull request #22 from ilelann/fix_cmake_include_dirs

fix cmake include directories at target level
diff --git a/CMakeLists.txt b/CMakeLists.txt
index ab557ad..32bfefd 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 2.8)
+cmake_minimum_required(VERSION 2.8.12)
 project(double-conversion)
 
 # pick a version #