[DOCS] Fix minor wrong lambda expression example.

It's a really minor issue but there is an example with wrong lambda-expression usage in `SQLContext.scala` like as follows.

```
sqlContext.udf().register("myUDF",
       (Integer arg1, String arg2) -> arg2 + arg1),  <- We have an extra `)` here.
       DataTypes.StringType);
```

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #7187 from sarutak/fix-minor-wrong-lambda-expression and squashes the following commits:

a13196d [Kousuke Saruta] Fixed minor wrong lambda expression example.

Author: sarutak

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

@@ -274,7 +274,7 @@ class SQLContext(@transient val sparkContext: SparkContext)
    * Or, to use Java 8 lambda syntax:
    * {{{
    *   sqlContext.udf().register("myUDF",
-   *       (Integer arg1, String arg2) -> arg2 + arg1),
+   *       (Integer arg1, String arg2) -> arg2 + arg1,
    *       DataTypes.StringType);
    * }}}
    *