a '-corrected black holes in String Theory

The authors would like to thank S. Chimento and A. Ruipérez for many useful conversations. This work has been supported in part by the MINECO/FEDER, UE grants FPA2015-66793-P and FPA2015-63667-P, by the Italian INFN and by the Spanish Research Agency (Agencia Estatal de Investigación) through the grant IFT Centro de Excelencia Severo Ochoa SEV-2016-0597. The work of PAC was funded by Fundación la Caixa through a “la Caixa - Severo Ochoa” international pre-doctoral grant. PAC also thanks Perimeter Institute “Visiting Graduate Fellows” program. Research at Perimeter Institute is supported by the Government of Canada through the Department of Innovation, Science and Economic Development and by the Province of Ontario through the Ministry of Research, Innovation and Science. TO wishes to thank M.M. Fern´andez for her permanent support.