fix download of first *.min.js.map files

[smartiniOnGitHub]

In the plugin, release 1.2.5 there is a small problem (in my usage of resources plugin, or in resources plugin ?) when Developer Tools try to download *.min.js.map files, it seems that first is get from a wrong url so it's not downloaded, but others are requested from the right url ... so only the first is missing.

See here for more info:
http://grails.1312388.n4.nabble.com/Resource-plugin-can-I-bundle-js-map-files-tp4652612.html

[smartiniOnGitHub]

Should be solved by the merge from #14