Remove leftovers from Travis CI

These days utop is using GitHub Actions.

.travis.yml

@@ -1,20 +0,0 @@
-language: c
-sudo: required
-install: wget https://raw.githubusercontent.com/ocaml/ocaml-ci-scripts/master/.travis-opam.sh
-script: bash -ex .travis-opam.sh
-env:
-  global:
-  - PACKAGE=utop
-  matrix:
-  - OCAML_VERSION=4.03
-  - OCAML_VERSION=4.04
-  - OCAML_VERSION=4.05
-  - OCAML_VERSION=4.06
-  - OCAML_VERSION=4.07
-  - OCAML_VERSION=4.08
-  - OCAML_VERSION=4.09
-  - OCAML_VERSION=4.10
-  - OCAML_VERSION=4.11.0+trunk OCAML_BETA=enable
-os:
-  - linux
-  - osx

README.md

@@ -1,3 +1,5 @@
+[![Build Status](https://github.com/ocaml-community/utop/workflows/Test%20in%20Nix/badge.svg)](https://github.com/ocaml-community/utop/actions/workflows/test-in-nix.yml)
+
 utop — a universal toplevel (i.e., REPL) for OCaml
 ==================================================
 
@@ -8,8 +10,6 @@ sensitive completion, colors, and more.
 
 It integrates with the Tuareg and typerex modes in Emacs.
 
-[![Travis build Status](https://travis-ci.org/ocaml-community/utop.svg?branch=master)](https://travis-ci.org/ocaml-community/utop)
-
 ![Screenshot](screenshot.png)
 
 Installation via opam