Plugin executes out of order relative to other serverless plugins

[jhslinkman]

Consider a serverless.yml

...
plugins:
    - serverless-stack-ouput
    - other-plugin

custom:
  output:
    file: stack-output.yml
...

where other-plugin processes stack-output.yml output by this file. As it's currently implemented, other-plugin will being processing before serverless-stack-output finished. The offending line is in the StackOutputPlugin#process method. If that method is changed to return a promise, everything works as expected.

[anttiviljami]

Since the original package doesn't seem to be maintained. I've merged #17 + #19 and published on npm under @anttiviljami/serverless-stack-output

[ismarslomic]

Any chance this can be merged to this original package?