Update to Lucene 4.8

Closes #30.
(cherry picked from commit bf7cc95)

src/main/java/org/elasticsearch/index/analysis/KuromojiPartOfSpeechFilterFactory.java

@@ -48,7 +48,7 @@ public class KuromojiPartOfSpeechFilterFactory extends AbstractTokenFilterFactor
 
     @Override
     public TokenStream create(TokenStream tokenStream) {
-        return new JapanesePartOfSpeechStopFilter(Version.LUCENE_44, tokenStream, stopTags);
+        return new JapanesePartOfSpeechStopFilter(Version.LUCENE_48, tokenStream, stopTags);
     }
 
 }

src/main/java/org/elasticsearch/indices/analysis/KuromojiIndicesAnalysis.java

@@ -94,7 +94,7 @@ public class KuromojiIndicesAnalysis extends AbstractComponent {
 
                     @Override
                     public TokenStream create(TokenStream tokenStream) {
-                        return new JapanesePartOfSpeechStopFilter(Version.LUCENE_44,
+                        return new JapanesePartOfSpeechStopFilter(Version.LUCENE_48,
                                 tokenStream, JapaneseAnalyzer
                                 .getDefaultStopTags());
                     }