configure travis ci in order to trace how fetch work at different cases

[atherdon]

Is your feature request related to a problem? Please describe.
I'm always frustrated when a new release of fetch plugin don't work fine at all situations.
E.g. it might work at plain js modules and at expressjs server, but crashing at React project. or backward. for sure, it partially related to our rollup setup. but right now this is not a main subject here. my goal is to setup a good CI enviroment, that will save time for us, when we make a new release, and we don't need to worry about rechecking each place, where we have this module right now. I'm 100% sure that Travis CI support this feature. we just need to find a cool example, tweak travis.yml file and do it.

Describe the solution you'd like
We add "something" at travis.yml that will install "stuff" 3 times(our 3 cases)

• when we testing at express.js - we just install express server + fetch and run express server(will it work? not clear)
• when we testing at React - we installing CRA and fetch inside and check it as well.
• run a plan js case test.

Describe alternatives you've considered
Maybe, just maybe - when we'll researching this problem, we'll figure out that Travis is not the best solution, and we'll check what Circle CI is proposing to their users. and we'll change our workflow and replace old, working ok Travis CI with a new modern Circle CI

Additional context

1. we should read docs of Travis CI
   and https://medium.com/@bezgachev/6-simple-steps-to-automatically-test-and-deploy-your-javascript-app-to-github-pages-c4c32a34bcb1
2. Check if this will be enough to catch issues, that we have right now.
3. maybe, some of the problems will go when i'll update our rollup workflow, but we always can break something and see if this will be caught by our CI.