Minor Change adding CAPABILITY_AUTO_EXPAND

[JPurrier]

SUMMARY I added the additional capability 'CAPABILITY_AUTO_EXPAND' I found this was a requirement for the stack i was deploying. So I imagine it will be useful for others.

ISSUE TYPE Bugfix Pull Request The module was missing the ability to add the capability CAPABILITY_AUTO_EXPAND COMPONENT NAME Small edit to the cloudformation_stack_set module

ADDITIONAL INFORMATION adds CAPABILITY_AUTO_EXPAND to the available options in the list