update snapshot links

Bintray shut down so we no longer have write access to oss.jfrog.org.
So we've set up a new instance for ev3dev.

Author: dlech

docs/getting-started.md

@@ -291,4 +291,4 @@ favorite language is probably supported. Pick your language and write some code!
 [microSDHC]: https://en.wikipedia.org/wiki/Secure_Digital#SDHC
 [microSDXC]: https://en.wikipedia.org/wiki/Secure_Digital#SDXC
 [releases]:https://github.com/ev3dev/ev3dev/releases
-[nightly]:https://oss.jfrog.org/list/oss-snapshot-local/org/ev3dev/brickstrap/
+[nightly]:https://ev3dev.jfrog.io/artifactory/snapshots/

downloads.md

@@ -151,7 +151,7 @@ redirect_from: /download/
             want to try out the latest new features and bug fixes.
         </p>
         <div class="margin-top-md">
-            <a class="btn btn-md btn-primary" href="https://oss.jfrog.org/list/oss-snapshot-local/org/ev3dev/brickstrap/">
+            <a class="btn btn-md btn-primary" href="https://ev3dev.jfrog.io/artifactory/snapshots/">
                 <span class="glyphicon glyphicon-link"></span>
                 Snapshots
             </a>