First, I want to remark that .abignore is fully respected in AppBuilder command-line interface and the AppBuilder package for Sublime Text and only using these tools will affect the output package.
I want to discuss the code you are using:
#The following rule excludes the grunt files and tasks
The first line gruntfile.js
will only ignore this file in the root folder and the second will ignore all json files again in the root. Be sure that the path to the files is right in order to exclude them from the package.
If you still have troubles to ignore files please attach your project to your private ticket with ID 907847 so we can take a look at it.