Revert "Remove travis"

This reverts commit 5e35a91e.

.travis.yml

+jobs:
+  include:
+    - os: osx
+      osx_image: xcode10.1
+      language: generic
+      env: ARTIFACT=x86_64-apple-darwin-10.13-ghcup
+
+    - os: osx
+      osx_image: xcode11.3
+      language: generic
+      env: ARTIFACT=x86_64-apple-darwin-10.14-ghcup
+
+script: ".travis/build.sh"
+
+deploy:
+  provider: releases
+  api_key:
+    secure: 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
+  file: $ARTIFACT
+  on:
+    repo: haskell/ghcup-hs
+    tags: true
+  skip_cleanup: true
+  draft: true
+

.travis/build.sh

+#/bin/sh
+
+set -ex
+
+## install ghc via old ghcup
+
+mkdir -p ~/.ghcup/bin
+curl https://gitlab.haskell.org/haskell/ghcup/raw/master/ghcup > ~/.ghcup/bin/ghcup
+chmod +x ~/.ghcup/bin/ghcup
+
+export PATH="$HOME/.ghcup/bin:$PATH"
+
+ghcup install 8.8.3
+ghcup install-cabal 3.2.0.0
+ghcup set 8.8.3
+
+
+## install ghcup
+
+cabal update
+cabal build
+cp "$(cabal new-exec --verbose=0 --offline sh -- -c 'command -v ghcup')" "./${ARTIFACT}"