Include <string> for std::string

[heirecka]

Fixes building with gcc 10.

Fixes Kurento/bugtracker#571

Signed-off-by: Heiko Becker heirecka@exherbo.org

What is the current behavior you want to change?

What is the new behavior provided by this change?

How has this been tested?

cmake && make (with gcc10)

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist

• I have read the Contribution Guidelines
• I have added an explanation of what the changes do and why they should be included
• I have written new tests for the changes, as applicable, and have successfully run them locally

[jenkinskurento]

Hi there, thanks for your Pull Request!

A Kurento member needs to verify that this patch is reasonable to test. In case it is, they should write a comment with the phrase test this please. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by Kurento members will still work. Regular contributors can be whitelisted to skip this step.