`WriteFiles` should ensure files' full paths exist

[Andy George]

For example, creating /etc/services/versions should also create /etc/services/ if it does not exist.

Current error:

/etc/services/versions
panic: open /etc/services/versions: no such file or directory

goroutine 1 [running]:
main.check(...)
	repos/injection/go/injection.go:198
main.main()
	repos/injection/go/injection.go:70 +0x1ee