feat(package.json): upgrade to "marker-clusterer-plus@^2.1.4"

* Closes #255
* Closes #259 
* Thanks to @pirate, @wedneyyuri and @michalkozminski

Author: pirate

package.json

@@ -85,7 +85,7 @@
     "google-maps-infobox": "^1.1.13",
     "invariant": "^2.1.1",
     "lodash.isequal": "^3.0.4",
-    "marker-clusterer-plus": "^2.1.2",
+    "marker-clusterer-plus": "^2.1.4",
     "react-prop-types-element-of-type": "^2.1.0",
     "scriptjs": "^2.5.8",
     "warning": "^2.1.0"