build: use older version of Karma to avoid bug

* karma-runner/karma#3226

package.json

@@ -44,7 +44,7 @@
     "husky": "^1.2.0",
     "istanbul-instrumenter-loader": "^3.0.1",
     "jasmine-core": "^3.3.0",
-    "karma": "^3.1.3",
+    "karma": "3.1.1",
     "karma-chrome-launcher": "^2.2.0",
     "karma-coverage-istanbul-reporter": "^2.0.4",
     "karma-jasmine": "^2.0.1",