Fix jest test in CI

Jest runs out of memory when run in Docker, possibly because of a memory
leak in ts-jest.

The tests will now run after the build, on the built *.js files. As a
consequence, the jest tests will run faster because ts-jest will no
longer be invoked in ci.

Check the package.json test:ci script for more info.

https://github.com/facebook/jest/issues/7874
https://github.com/facebook/jest/issues/9081

.drone.yml

@@ -10,10 +10,10 @@ steps:
       - npm install
       - npm run lint
       - npm run bootstrap
-      - npm run jest
+      - npm run test:ci
       - npm run esm
 ---
 kind: signature
-hmac: ccaae75bbb4cb95e9e82761ffaf6fe1293e5a35b4b7dca077f38837e44e567fa
+hmac: 2a4dd894429afc6c3908a5d53cab57cac9a3918260a01e3f845db9aba53d6316
 
 ...