Confusing wording about environment variables

[urbantom]

File: engine/reference/builder.md
Regarding the paragraph "The ENV instruction has two forms. The first form, ENV , will set a single variable to a value. The entire string after the first space will be treated as the - including characters such as spaces and quotes."

I suggest to consider the variant "The entire string after the second space will be treated as the ..." as the proper one.

[rubabzs]

There's no such file in this repo. However, it is present under docker/docs/reference/builder.md. How to go about this? Thanks!

[prashant171992]

@urbantom i raised a PR(#2849) to merge in docker:v1.13 as this file not present in master branch

[urbantom]

Thanks in behalf of all newbies. ;-)