Update copyright from 2017 to 2018

Author: tysongach

LICENSE.md

@@ -1,6 +1,6 @@
 The MIT License (MIT)
 
-Copyright © 2011-2017 [thoughtbot, inc.](http://thoughtbot.com)
+Copyright © 2011-2018 [thoughtbot, inc.](http://thoughtbot.com)
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the “Software”), to deal

README.md

@@ -206,7 +206,7 @@ See the [contributing] document. Thank you, [contributors]!
 
 ## License
 
-Bourbon is copyright © 2011-2017 [thoughtbot, inc.][thoughtbot] It is free
+Bourbon is copyright © 2011-2018 [thoughtbot, inc.][thoughtbot] It is free
 software, and may be redistributed under the terms specified in the [license].
 
   [license]: LICENSE.md

core/_bourbon.scss

@@ -1,6 +1,6 @@
 // Bourbon 5.0.0-beta.8
 // http://bourbon.io
-// Copyright 2011-2017 thoughtbot, inc.
+// Copyright 2011-2018 thoughtbot, inc.
 // MIT License
 
 @import "bourbon/helpers/buttons-list";