Bump mobx from 6.3.0 to 6.4.2

Author: rgdelato

package.json

@@ -26,7 +26,7 @@
     "jest": "^27.2.0",
     "jquery": "^2.2.4",
     "lodash": "^4.17.21",
-    "mobx": "^6.3.0",
+    "mobx": "^6.4.2",
     "react": "^15.7.0",
     "react-dom": "^15.7.0",
     "react-router": "^4.3.1",