update date in README

[xlgao-zju]

update date in README from 2014 to 2015

Signed-off-by: xlgao-zju xlgao@zju.edu.cn

[crosbymichael]

LGTM

[hqhq]

LGTM

[thaJeztah]

I wonder if this is correct; perhaps it should be either 2014 (if that's the year the original code was written), or 2014-2016. But IANAL, so worth checking

[hqhq]

@thaJeztah Thanks, after some checking, I think you are right, according to https://softwarefreedom.org/resources/2012/ManagingCopyrightInformation.html

Under U.S. law, a properly formatted copyright notice should include: 1) the © symbol, the word “Copyright”, or the abbreviation “Copr.”; 2) the year of the work’s first publication; and 3) the name of the copyright owner. For example, “Copyright 2012 Jane Hacker.” If contributions were made during several years, use commas to separate nonconsecutive years and hyphens to indicate contributions over several consecutive years, e.g.: “Copyright 2007, 2009, 2010 – 2012 Jane Hacker.”

I think we should keep the copyright notification as it was. I'll revert it.