Add support for building with Travis CI

[tylerhall]

Per request from @syddo here #4

[tylerhall]

So, I'm not a Travis CI user normally and don't really have any experience with their platform. I quickly cobbled together a .travis.yml file that I thought might work for macOS, but the first build failed. If someone wants to take a look, that'd be great.

That said, this project doesn't have any tests included, so other than Travis verifying that the build succeeds, it's not going to do much. But I'm happy to include Travis CI support regardless. Certainly can't hurt.

[funkyboy]

@tylerhall The lock file in the repo is generated using Cocoapods 1.9.1 (https://github.com/tylerhall/DefaultApp/blob/master/Podfile.lock#L35) while the Travis image you are using still has Cocoapods 1.8.4 (as reported here https://travis-ci.org/github/tylerhall/DefaultApp/builds/663623217#L638)

Solutions are (either):

• use Cocoapods 1.8.4 in your repo
• update Cocoapods (via a gem install cocoapods -v 1.9.1) on Travis before the build is run, using something like

before_install:
 - gem install cocoapods -v 1.9.1

in your travis file.

Hope this helps.

[tylerhall]

Thanks for that, @funkyboy. I'll give it a try.