use travis to check build and run tests

[explodecomputer]

https://travis-ci.org/

See here for example https://github.com/mrcieu/ieugwasr

[yoonsucho]

use_travis()
✔ Writing '.travis.yml'
✔ Adding '^\.travis\.yml$' to '.Rbuildignore'
● Turn on travis for your repo at https://travis-ci.org/profile/explodecomputer
● Copy and paste the following lines into 'C:/Users/yc16575/OneDrive - University of Bristol/Documents/tryx/README.md':

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