Fix for build issues when the job description has "invalid" characters.

I had some problems with the StashNotifier. On some builds the INPROGRESS worked but the SUCCESSFUL not. After looking into the differences, the thing I found was that the jobs which weren't placed on SUCCESSFUL had a custom build description which among others had "/" in it.

This change should fix it!

(somehow I can't use the plugin when I build it myself: class org.jenkinsci.plugins.stashNotifier.StashNotifier is missing its descriptor)