ci(jest): remove detectOpenHandles flag

The detectOpenHandles flag was added to help pin down an issue that we
were facing with some of our tests a while back. This flag comes with a
very high performance penalty and is no longer needed in our setup.

package.json

@@ -34,7 +34,7 @@
     "start-main-dev": "cross-env HOT=1 NODE_ENV=development electron -r babel-register ./app/main.dev",
     "start-renderer-dev": "node --trace-warnings -r babel-register ./node_modules/webpack-serve/lib/cli.js --config internals/webpack/webpack.config.renderer.dev.js",
     "test": "npm run lint && npm run lint-styles && npm run flow && npm run build && npm run test-unit && npm run test-e2e",
-    "test-base": "cross-env NODE_ENV=test BABEL_DISABLE_CACHE=true ELECTRON_DISABLE_SECURITY_WARNINGS=true node --trace-warnings ./node_modules/jest/bin/jest --detectOpenHandles",
+    "test-base": "cross-env NODE_ENV=test BABEL_DISABLE_CACHE=true ELECTRON_DISABLE_SECURITY_WARNINGS=true node --trace-warnings ./node_modules/jest/bin/jest",
     "test-unit": "npm run test-base -- ./test/unit",
     "test-e2e": "npm run test-base -- ./test/e2e",
     "test-ci": "npm run test-e2e && npm run test-unit"