chore(project): detect unresolved lint rules

This ensures we don't accidently require files in the lib directory
via the global `lib` import. That stuff works during tests but does
not work in the final bundle.

Considerations: This plugin adds some runtime overhead to our linting
process.

lib/.eslintrc

@@ -0,0 +1,8 @@
+{
+  "plugins": [
+    "import"
+  ],
+  "rules": {
+    "import/no-unresolved": "error"
+  }
+}

package.json

@@ -45,6 +45,7 @@
     "del": "^3.0.0",
     "eslint": "^5.7.0",
     "eslint-plugin-bpmn-io": "^0.6.0",
+    "eslint-plugin-import": "^2.14.0",
     "execa": "^1.0.0",
     "istanbul-instrumenter-loader": "^3.0.1",
     "karma": "^3.1.1",