Better approach to fixing TermStats.TermText to fix one failing unit …

…test.

src/Lucene.Net.Misc/Misc/TermStats.cs

@@ -25,7 +25,7 @@ namespace Lucene.Net.Misc
     /// </summary>
     public sealed class TermStats
     {
-        public readonly BytesRef TermText;
+        public BytesRef TermText { get; private set; }
         public string Field { get; set; }
         public int DocFreq { get; set; }
         public long TotalTermFreq { get; set; }