support customized analyzer with no-argument constructor.

As we know, when using sensei-hadoop-indexing tool to build index, must specify the value of "sensei.document.analyzer.version" in the job configuration file.

If missing that parameter, SenseiMapper will throw an IllegalstateException. Because it assumed that the analyzer object must have an constructor with only one parameter which type is Org.Apache.Lucene.Util.Version.

But some open-sourced analyzers only have an no-argument constructor (e.g. IKAnalyzer, a chinese analyzer).

So I think the conf parameter sensei.document.analyzer.version is not mendatory.