[minor] travis: only test for Changes/testsuite on pull requests
[minor] travis: only test for Changes/testsuite on pull requests

gerdstolpmann/ocaml,gerdstolpmann/ocaml,yunxing/ocaml,msprotz/ocaml,yunxing/ocaml,gerdstolpmann/ocaml,msprotz/ocaml,yunxing/ocaml,msprotz/ocaml,msprotz/ocaml,gerdstolpmann/ocaml,yunxing/ocaml,msprotz/ocaml,gerdstolpmann/ocaml,yunxing/ocaml