Updated to use the output_directory from gym if provided

[asoneji]

In our gym config, we have provided output_directory dir. When using IPASizeProvider we got the follwoing error:

[17:28:41]: $ ../Pods/SwiftInfo/bin/swiftinfo
[17:28:47]: ▸ * Extracting ipa_size
[17:28:47]: ▸ * **ipa_size:** .ipa not found! Attempted to find .ipa at: ../build/

I noticed is not using the output_directory dir from gym and instead, it is expecting the ipa to be inside the ./build folder.

[rockbruno]

Seems like we could to add a path parameter to IPASizeProvider. Should be an easy fix 👍