fixed public c++11 flag

CMakeLists.txt

@@ -13,7 +13,7 @@ if (MSVC)
     target_compile_options(glm-extras PUBLIC /MP)
 else()
     target_compile_options(glm-extras PRIVATE -Wall -Werror)
-    target_compile_options(glm-extras PUBLIC
+    target_compile_options(glm-extras PRIVATE
         $<$<COMPILE_LANGUAGE:CXX>:-std=c++11>
         -march=native
         -fPIC