[fix] Use 'deep-equal' to compare whether arrays are equal

Using `JSON.stringify()`, when a marker has a popup created with `L.popup()`,
rather than a straight string, then the following error is thrown:

    Uncaught TypeError: Converting circular structure to JSON
        at JSON.stringify (<anonymous>)
        at isArraysEqual

See #55

dist/react-leaflet-markercluster.js

@@ -20,6 +20,10 @@ var _leaflet = require('leaflet');
 
 var _leaflet2 = _interopRequireDefault(_leaflet);
 
+var _deepEqual = require('deep-equal');
+
+var _deepEqual2 = _interopRequireDefault(_deepEqual);
+
 function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
 
 function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }
@@ -42,7 +46,7 @@ function havingDeprecatedProps(markers) {
 
 // NOTE: Helpers
 function isArraysEqual(firstArray, secondArray) {
-  return JSON.stringify(firstArray) === JSON.stringify(secondArray);
+  return firstArray.length === secondArray.length && (0, _deepEqual2.default)(firstArray, secondArray);
 }
 
 function removeMarkersWithSameCoordinates(markers) {
@@ -252,4 +256,4 @@ MarkerClusterGroup.propTypes = {
 
 MarkerClusterGroup.defaultProps = {
   markers: []
-};
+};

package.json

@@ -97,5 +97,8 @@
     "prop-types": "^15.5.7",
     "react": "^15.0.0 || ^16.0.0",
     "react-leaflet": "^1.4.0"
+  },
+  "dependencies": {
+    "deep-equal": "^1.0.1"
   }
 }

src/react-leaflet-markercluster.js

@@ -3,6 +3,7 @@ import PropTypes from 'prop-types';
 
 import { LayerGroup } from 'react-leaflet';
 import L from 'leaflet';
+import deepEqual from 'deep-equal';
 
 require('leaflet.markercluster');
 
@@ -16,7 +17,7 @@ function havingDeprecatedProps(markers) {
 
 // NOTE: Helpers
 function isArraysEqual(firstArray, secondArray) {
-  return (JSON.stringify(firstArray) === JSON.stringify(secondArray));
+  return firstArray.length === secondArray.length && deepEqual(firstArray, secondArray);
 }
 
 function removeMarkersWithSameCoordinates(markers) {