Add SubversionDownloadStrategy#source_modified_time

[vladshablinsky]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully ran brew tests with your changes locally?

Description

Implement SubversionDownloadStrategy#source_modified_time from #81

[MikeMcQuaid]

Looks good to me 👍 @xu-cheng, any thoughts?

[xu-cheng]

LGTM. Sorry for late response

[UniqMartin]

Sorry for the late comment! I wonder to what extent #171 (comment) is also applicable here and whether it would be a good idea to extract the information from svn info --xml instead …

[xu-cheng]

cc @vladshablinsky

svn info --xml seems to be a better approach. You can parse XML using REXML::XPath.
e.g.

require "rexml/document"
xml = REXML::Document.new(Utils.popen_read("svn", "info", "--xml", cached_location.to_s))
Time.parse REXML::XPath.first(xml, "//date/text()")

[vladshablinsky]

@xu-cheng I knew about this option and thought that REXML does pretty much the same things like regular expression matching. However it could be more flexible if svn's log output changes in new versions, so I'll open a new PR. Thanks!

@UniqMartin seems there is no way to change the date output format.