tests: add maxWorker option to Jest so it doesn't just break on some …

…linux PC for some reasons

package.json

@@ -67,7 +67,7 @@
     "test:integration:firefox:watch": "node tests/integration/run.js --bfirefox --watch",
     "test:memory": "node tests/memory/run.js --bchromehl",
     "test:memory:chrome:watch": "node tests/memory/run.js --bchrome --watch",
-    "test:unit": "jest",
+    "test:unit": "jest --maxWorkers=5",
     "test:unit:coverage": "jest --coverage",
     "update-version": "npm run version --git-tag-version=false",
     "version": "./scripts/update-version"