espeak: fix legal info

The file is License.txt, not License.txt (so, the other english). Fixes:
http://autobuild.buildroot.net/results/a8b/a8b2b93e96901fe4fdfb64e1941c5c45bd52c742/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>