Make .ipa input optional when .dSYM is given

[MiloszFilimowski]

According to API documentation it is possible to upload an app without .ipa if .dSYM is given. This helps when using HockeyApp only for crash reporting.

This PR introduces a small change to allow for dsym_path to be passed without ipa_path

[viktorbenei]

Thanks for the PR @MiloszFilimowski ! We'll review this ASAP! :)

[viktorbenei]

Just a quick note until the review: you can use your own version of this step with the git:: style reference (http://devcenter.bitrise.io/bitrise-cli/steps/#special-step-sources):

Instead of:

    steps:
    - hockeyapp-deploy:

use:

    steps:
    - git::https://github.com/MiloszFilimowski/steps-hockeyapp-deploy.git@optional-ipa:

[MiloszFilimowski]

Thanks @viktorbenei ;)

[viktorbenei]

Any time @MiloszFilimowski ;)

[godrei]

Hi @MiloszFilimowski ,
thanks for the PR, your changes looks great to me!