fix dependency (#344)

Author: nicolaskruchten

package.json

@@ -12,6 +12,7 @@
     "draft-js-import-html": "^1.2.1",
     "draft-js-utils": "^1.2.0",
     "fast-isnumeric": "^1.1.1",
+    "immutability-helper": "^2.6.4",
     "plotly-icons": "^1.1.3",
     "plotly.js": "^1.33.0",
     "prop-types": "^15.5.10",
@@ -51,7 +52,6 @@
     "fs": "^0.0.1-security",
     "gl": "^4.0.4",
     "glob": "^7.1.2",
-    "immutability-helper": "^2.6.4",
     "jest": "^21.2.1",
     "jest-cli": "^22.0.4",
     "mkdirp": "^0.5.1",