Format of main.buildDate has been locale-dependent,
and is now ISO-8601 compliant.

Caddy displayed with ```-version``` something like (mind the datetime format):

    Caddy 0.8.2 (+591b2090 Fri Mar 18 21:22:55 UTC 2016)
     2 files changed, 9 insertions(+), 4 deletions(-)
    build.bash
    main.go

which is now:

    Caddy 0.8.2 (+591b2090 2016-03-18 21:22:55Z)
     2 files changed, 9 insertions(+), 4 deletions(-)
    build.bash,main.go

See also:

 * http://wiki.bash-hackers.org/scripting/obsolete
 * https://google.github.io/styleguide/shell.xml
 * https://xkcd.com/1179/