Add CI steps

Author: ulrikstrid

.circleci/config.yml

@@ -27,3 +27,15 @@ jobs: # a collection of steps
       - run: # run tests
           name: test
           command: npm test
+
+      - run:
+          name: Install esy
+          command: sudo npm -g install esy@latest --unsafe-perm
+
+      - run:
+          name: Install dependencies
+          command: esy install
+
+      - run:
+          name: Build with esy
+          command: esy build