Update Makefile

Makefile

 # the prefix of the generated executable file
 # the prefix of the generated executable file
-PREFIX = NiuTrans
-NIUTRANS_EXE := $(PREFIX).Tensor
+NIUTRANS_EXE := NiuTensor
 
 
 # code path and generated file path
 # code path and generated file path
 ROOT = .
 ROOT = .