update COPYING (#789)

Author: farindk

COPYING

@@ -1,5 +1,5 @@
 * The library `libheif` is distributed under the terms of the GNU Lesser General Public License.
-* The sample applications are distributed under the terms of the MIT License.
+* The sample applications and the Go and C++ wrappers are distributed under the terms of the MIT License.
 
 License texts below and in the `COPYING` files of the corresponding subfolders.