Add libpostal in mason

[manoharuss]

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[manoharuss]

Hi @springmeyer when you have time, could you review this PR for installing libpostal from mason.

build works for me locally on osx with

./mason build libpostal 1.1-alpha

I wasn't able to use ./mason trigger libpostal 1.1-alpha as I didn't not have MASON_TRAVIS_TOKEN variable.

Travis: The expat installation seems return a md5 sha mismatch. I do not completely understand what happens if i directly update the sha there. could you also help with that.
https://travis-ci.org/github/mapbox/mason/builds/711237110

[mattficke]

Travis: The expat installation seems return a md5 sha mismatch. I do not completely understand what happens if i directly update the sha there. could you also help with that.

@manoharuss a mismatched hash like that usually means there was a problem with the download. I retried the build and it succeeded.

I wasn't able to use ./mason trigger libpostal 1.1-alpha as I didn't not have MASON_TRAVIS_TOKEN variable.

You can use the travis gem to fetch this token, there are instructions in the readme: https://github.com/mapbox/mason#trigger