change CC license to by-sa

@@ -47,17 +47,17 @@
 					</p>
 					<p>
 					All other work is licensed under a
-					<a href="http://creativecommons.org/licenses/by/4.0/" rel="license">
+					<a href="http://creativecommons.org/licenses/by-sa/4.0/" rel="license">
 						Creative Commons Attribution 4.0 International License
 					</a>.
 					</p>
 				</div>
-				<a href="http://creativecommons.org/licenses/by/4.0/" rel="license">
+				<a href="http://creativecommons.org/licenses/by-sa/4.0/" rel="license">
 					<img alt="Creative Commons License"
 					     style="border-width:0"
 					     width="88"
 					     height="31"
-					     src="https://i.creativecommons.org/l/by/4.0/88x31.png" />
+					     src="https://i.creativecommons.org/l/by-sa/4.0/88x31.png" />
 				</a>
 				<a href="http://www.gnu.org/licenses/gpl-3.0.en.html" rel="license">
 					<%= image_tag("gpl-v3-red.png", height: "31", width: "62") %>