Fix badge using old license

README.md

@@ -1,6 +1,6 @@
 # Pinout.xyz
 
-<a rel="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/"><img alt="Creative Commons License" style="border-width:0" src="https://i.creativecommons.org/l/by-nc-sa/4.0/88x31.png" /></a>
+<a rel="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/"><img alt="Creative Commons License" style="border-width:0" src="https://i.creativecommons.org/l/by-sa/4.0/88x31.png" /></a>
 
 [Pinout.xyz](http://pinout.xyz/) is the successor to the popular Pi pinout website originally hosted on [http://pi.gadgetoid.com/pinout](http://pi.gadgetoid.com/pinout).