Wrong FileInfo.modTime generation

[dmke]

Hi,

I've noticed a small issue with the FileInfo.modTime generation. It is a bit annoying because it prevents proper client-side caching when serving the contents via HTTP.

In the generated file, I find this entry:

FileInfo{
	modTime: time.Unix(1504547519, 1504547519143839891),
	// etc.
}

However, time.Unix will return 2065-05-09T12:43:58+01:00, the correct value (ignoring time zones) is:

$ stat -c %y ui/build/style.css
2017-09-04 19:51:59.143839891 +0200

While the documentation of time.Unix states

It is valid to pass nsec outside the range [0, 999999999]

it does not mention the implementation detail that it adds nsec / 1e9 to the sec value. Hence the generated FileInfo should be in either of these forms:

time.Unix(0, 1504547519143839891) // 0, nsec
time.Unix(1504547519, 143839891)  // nsec/1e9, nsec%1e9

I believe the first form should work on any Go release (the crucial part in the implementation of Go1 and Go1.9 has stayed the same).