duplicate entry: org/appcelerator/titanium/gen/bindings.json

I have 2 modules add into the project,it throw error when use the 2 modules in the same time(it run ok when deleted one of the modules):

[ERROR] :  Failed to sign apk:
[ERROR] Application Installer abnormal process termination. Process exit value was 1

java.util.zip.ZipException: duplicate entry: org/appcelerator/titanium/gen/bindings.json

I have no idea how this happened, can anybody help me please ,thanks

the bindings.json files is like this

{"modules":{"titutorial.demo1.Demo1Module":{"apiName":"Demo1"}}...

{"modules":{"titutorial.demo2.Demo2Module":{"apiName":"Demo2"}}...