vendor: Update go-toml

vendor: Update go-toml

Slightly better:

```
benchmark                                                                                                                      old ns/op     new ns/op     delta
BenchmarkSiteBuilding/frontmatter=TOML|num_root_sections=1|num_pages=1000|tags_per_page=20|shortcodes=false|render=false-4     204522447     200702508     -1.87%

benchmark                                                                                                                      old allocs     new allocs     delta
BenchmarkSiteBuilding/frontmatter=TOML|num_root_sections=1|num_pages=1000|tags_per_page=20|shortcodes=false|render=false-4     1943677        1784437        -8.19%

benchmark                                                                                                                      old bytes     new bytes     delta
BenchmarkSiteBuilding/frontmatter=TOML|num_root_sections=1|num_pages=1000|tags_per_page=20|shortcodes=false|render=false-4     102665182     100925773     -1.69%
```