rn: fix crash when serializing calendar entries on iOS

Original PR: https://github.com/wmcmahan/react-native-calendar-events/pull/253

package-lock.json

       "integrity": "sha512-cuXIIv+dcG8a8qkTD8pMzeqOEZCO+UGKglZWIe1osve+yJslmCowYQff+bI9xa7NOt2w+Vtd4L3d9JonlSqODg=="
     },
     "react-native-calendar-events": {
-      "version": "github:jitsi/react-native-calendar-events#f621cbe97b182cfaca41545fd6b818a85d632506",
-      "from": "github:jitsi/react-native-calendar-events#f621cbe97b182cfaca41545fd6b818a85d632506"
+      "version": "github:jitsi/react-native-calendar-events#902e6e92d6bae450a6052f76ba4d02f977ffd8f2",
+      "from": "github:jitsi/react-native-calendar-events#902e6e92d6bae450a6052f76ba4d02f977ffd8f2"
     },
     "react-native-callstats": {
       "version": "3.61.0",

package.json

     "react-linkify": "1.0.0-alpha",
     "react-native": "0.60.5",
     "react-native-background-timer": "2.1.1",
-    "react-native-calendar-events": "github:jitsi/react-native-calendar-events#f621cbe97b182cfaca41545fd6b818a85d632506",
+    "react-native-calendar-events": "github:jitsi/react-native-calendar-events#902e6e92d6bae450a6052f76ba4d02f977ffd8f2",
     "react-native-callstats": "3.61.0",
     "react-native-google-signin": "2.0.0",
     "react-native-immersive": "2.0.0",