Run some tests on Travis still

While GitHub Actions are in beta, that CI workflow only runs if
contributors are also in the beta. Let's run some tests in Travis for
the time being.

.travis.yml

@@ -0,0 +1,27 @@
+branches:
+  except:
+    - master
+    - /v\d.+/
+language: node_js
+os:
+  - windows
+  - linux
+node_js:
+  - 12
+before_install: if [[ "$(npm -v)" != "6.9.0" ]] && [[ "${TRAVIS_OS_NAME}" != "windows" ]]; then npm install --global [email protected]; fi
+install: npm ci
+before_script: |
+  if [[ "${TRAVIS_OS_NAME}" != "windows" ]]; then
+    checksum=$(md5sum package-lock.json)
+    npm install --package-lock-only
+    if ! echo ${checksum} | md5sum --quiet -c -; then
+      echo "package-lock.json was modified unexpectedly. Please rebuild it using npm@$(npm -v) and commit the changes."
+      exit 1
+    fi
+  fi
+
+  if [[ "${TRAVIS_OS_NAME}" == "windows" ]]; then
+    git config core.symlinks true
+    git reset --hard
+  fi
+after_success: npx codecov --file=./coverage/lcov.info