CMakeLists: filename fix so everything works on case-sensitive filesystems

src/libslic3r/CMakeLists.txt

@@ -100,7 +100,7 @@ add_library(libslic3r STATIC
     Geometry.cpp
     Geometry.hpp
     Int128.hpp
-    KdTreeIndirect.hpp
+    KDTreeIndirect.hpp
     Layer.cpp
     Layer.hpp
     LayerRegion.cpp