add '.' for hex()

Author: adrian-wang

sql/core/src/main/scala/org/apache/spark/sql/functions.scala

@@ -1092,15 +1092,15 @@ object functions {
     greatest((columnName +: columnNames).map(Column.apply): _*)
 
   /**
-    * Computes hex value of the given column
+    * Computes hex value of the given column.
     *
     * @group math_funcs
     * @since 1.5.0
     */
   def hex(column: Column): Column = Hex(column.expr)
 
   /**
-   * Computes hex value of the given input
+   * Computes hex value of the given input.
    *
    * @group math_funcs
    * @since 1.5.0