!58 cell的cellType由Numeric修正为String

Merge pull request !58 from 4ook/master

@@ -476,7 +476,7 @@ public class ExcelUtil<T>
     {
         if (ColumnType.STRING == attr.cellType())
         {
-            cell.setCellType(CellType.NUMERIC);
+            cell.setCellType(CellType.STRING);
             cell.setCellValue(StringUtils.isNull(value) ? attr.defaultValue() : value + attr.suffix());
         }
         else if (ColumnType.NUMERIC == attr.cellType())