typo fix for document

Author: chunming-c

docs/columns.md

@@ -435,14 +435,14 @@ Furthermore, it also accepts a callback which takes **4** arguments and `String`
 const headerSortingClasses = (column, sortOrder, isLastSorting, colIndex) => { ... }
 ```
 
-* column: The value of current column.
-* sortOrder: The order of current sorting
-* isLastSorting: Is the last one of sorting.
-* colIndex: The index of the current column being processed in BootstrapTable.
+* `column`: The value of current column.
+* `sortOrder`: The order of current sorting
+* `isLastSorting`: Is the last one of sorting.
+* `colIndex`: The index of the current column being processed in BootstrapTable.
 
 ### <a name='headerSortingStyle'>headerSortingStyle - [Object | Function]</a>
 
-It's similiar to [headerSortingClasses](#headerSortingClasses). It allows to customize style of `header cell` which is sorting based on. `Object` or `callback` are acceptable. `callback` takes **4** arguments and an `Object` is expected to return:
+It's similiar to [headerSortingClasses](#headerSortingClasses). It allows to customize style of header cell which is sorting based on. An style `Object` and `callback` are acceptable. `callback` takes **4** arguments and an `Object` is expected to return:
 
 ```js
 const sortingHeaderStyle = {