[gnome-user-docs] Consistently use Unported licenses for GNOME docs

[Petr Kovář <pmkovar src gnome org>]

commit fd860d253126fe0dcfc163dc4e31eb0531687954
Author: Petr Kovar <pkovar redhat com>
Date:   Fri Jul 19 11:35:44 2019 -0700

    Consistently use Unported licenses for GNOME docs
    
    Legal notice refers to https://creativecommons.org/licenses/by/3.0/
    which describes the Unported license, so use that.
    
    Also, do not include mail address as these tend to get outdated.

 COPYING | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)
---
diff --git a/COPYING b/COPYING
index b8d3c0ca..51b04ab6 100644
--- a/COPYING
+++ b/COPYING
@@ -1,4 +1,3 @@
 This work is licenced under the Creative Commons Attribution 3.0
-United States License. To view a copy of this licence, visit
-http://creativecommons.org/licenses/by/3.0/ or send a letter to Creative
-Commons, 171 Second Street, Suite 300, San Francisco, California 94105, USA.
+Unported License. To view a copy of this license, visit:
+http://creativecommons.org/licenses/by/3.0/