Bump bundlex dependency to 1.4, fix for cross-compile on OSX.

[CJRChang]

Updated to use Bundlex.platform() to better support cross-compilation while on OSX.

[Noarkhh]

Hi!

I apologize for the wait. We've been busy addressing the issue you made us aware of in Bundlex: membraneframework/bundlex#124.

We concluded that having two public functions (Bundlex.get_target/0 and Bundlex.platform/0) was unnecessary and confusing. We chose to keep Bundlex.get_target/0 because it can detect cross-compilation and convey more information, such as the target's OS and architecture. These details are also conveniently provided when cross-compiling using Nerves.

We decided to deprecate Bundlex.platform/0, as Bundlex.get_target/0 can effectively replace it.

Thank you for your contribution! Even though I will be closing this PR, it prompted us to fix the underlying issue in Bundlex. Once Bundlex is upgraded to 1.5 here, cross-compilation will be fully supported :)

[Noarkhh]

I just updated the plugin to use Bundlex ~> 1.5, so this should now work :)