Update Makefile

Makefile

 # the prefix of the generated executable file
-PREFIX = NiuTrans
-NIUTRANS_EXE := $(PREFIX).Tensor
+NIUTRANS_EXE := NiuTensor
 
 # code path and generated file path
 ROOT = .
@@ -222,4 +221,4 @@ endif
 clean:
 	@echo "Cleaning object files"
 	@-rm -f $(OBJS)
-	
\ No newline at end of file
+