Update the year in README (2018)

Signed-off-by: Cédric Marie <cedric@hjuvi.lautre.net>

README

 Painted Shell: A collection of colorful settings and scripts for Bash shell.
 
-Written in 2013-2017 by Cédric Marie <cedric@hjuvi.lautre.net>
+Written in 2013-2018 by Cédric Marie <cedric@hjuvi.lautre.net>
 
 To the extent possible under law, the author(s) have dedicated all copyright
 and related and neighboring rights to this software to the public domain