folly: 2018.02.26.00 -> 2018.03.26.00

Semi-automatic update generated by https://github.com/ryantm/nixpkgs-update tools.

This update was made based on information from https://repology.org/metapackage/folly/versions.

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 2018.03.26.00 with grep in /nix/store/3gv71wva8lpjgwvi5rrdq4441xk112w7-folly-2018.03.26.00
- directory tree listing: https://gist.github.com/936223d2c5bbeea7a741d5500253330a