Add Kostiantyn Sokolovskyi to the AUTHORS. (flutter#147065)

This PR adds my name to AUTHORS.

Reference: [author:ksokolovskyi](https://github.com/flutter/flutter/issues?q=author%3Aksokolovskyi)

Author: ksokolovskyi

AUTHORS

@@ -121,3 +121,4 @@ Mahdi Bagheri <1839491@gmail.com>
 Mok Kah Wai <taboosun1996@gmail.com>
 Lucas Saudon <lsaudon@gmail.com>
 Om Phatak <everythingoutdated@gmail.com>
+Kostiantyn Sokolovskyi <sokolovskyi.konstantin@gmail.com>