closes https://github.com/assimp/assimp/issues/918: use correct lib

install name for macos.

code/CMakeLists.txt

@@ -809,7 +809,7 @@ SET_TARGET_PROPERTIES( assimp PROPERTIES
 )
 
 if (APPLE)
-  SET_TARGET_PROPERTIES( assimp PROPERTIES INSTALL_NAME_DIR "${CMAKE_INSTALL_PREFIX}/${LIB_INSTALL_DIR}")
+  SET_TARGET_PROPERTIES( assimp PROPERTIES INSTALL_NAME_DIR "${CMAKE_INSTALL_PREFIX}/${ASSIMP_LIB_INSTALL_DIR}")
 endif()
 
 # Build against external unzip, or add ../contrib/unzip so