folly: 2017.11.06.00 -> 2018.02.26.00

Semi-automatic update. These checks were done:

- built on NixOS
- Warning: no binary found that responded to help or version flags. (This warning appears even if the package isn't expected to have binaries.)
- found 2018.02.26.00 with grep in /nix/store/a1f6l0wcn1cw5v7ycmpdd21kmka3bxpg-folly-2018.02.26.00
- found 2018.02.26.00 in filename of file in /nix/store/a1f6l0wcn1cw5v7ycmpdd21kmka3bxpg-folly-2018.02.26.00