update manifest

MANIFEST.in

@@ -1,7 +1,9 @@
 recursive-include csrc *.cu
 recursive-include csrc *.h
+recursive-include csrc *.cuh
 recursive-include csrc *.cpp
 
 recursive-include flash_attn *.cu
 recursive-include flash_attn *.h
+recursive-include flash_attn *.cuh
 recursive-include flash_attn *.cpp