Update uglify-js to remove security warning

This does not change the code as it has already been compiled. Only done to remove the warning

Known security issues:
* https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-8857
* https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-8858

Author: schloerke

docs/libs/leaflet-markercluster/package.json

@@ -7,7 +7,7 @@
 		"jshint": "~2.1.3",
 		"mocha": "~1.10.0",
 		"karma": "~0.8.5",
-		"uglify-js": "~2.3.6",
+		"uglify-js": "~2.6.0",
 		"jake": "~0.5.16",
 		"magic-string": "^0.7.0",
 		"leaflet": "~1.0.3"