Summary
-------

Add the constant `RELEASE_10` to the `SourceVersion` `enum`.

Problem
-------

With a new release, a matching new  `SourceVersion` constant is needed.

Solution
--------
Add the new constant.

Specification
-------------

    -     RELEASE_9;
    +     RELEASE_9,
    +
    +    /**
    +     * The version recognized by the Java Platform, Standard Edition
    +     * 10.
    +     *
    +     * @since 10
    +     */
    +     RELEASE_10;