Include <string> for std::string (#25)
Include <string> for std::string (#25)

Fixes building with gcc 10.

Fixes https://github.com/Kurento/bugtracker/issues/571

Signed-off-by: Heiko Becker <173873dca5336bc5b879e1ef4b61928a4c3d3e1b@exherbo.org>
Kurento/kms-core,Kurento/kms-core,Kurento/kms-core,Kurento/kms-core