Update links to Relstorage 3.0 post. Fixes #508

Author: jamadden

docs/migration/migrate-to-3.0.rst

@@ -5,7 +5,7 @@
 A small migration is necessary for all schemas. It is accomplished
 automatically the first time RelStorage 3.0 is used. See `the release
 announcement
-<https://dev.nextthought.com/blog/2019/11/relstorage-30.html>`_ for
+<https://seecoresoftware.com/blog/2019/11/relstorage-30.html>`_ for
 details.
 
 Oracle

docs/performance.rst

@@ -18,7 +18,7 @@ RelStorage 3
 
 RelStorage 3 performance is substantially improved on many benchmarks.
 See `this post
-<https://dev.nextthought.com/blog/2019/11/relstorage-30.html#performance-improvements>`_
+<https://seecoresoftware.com/blog/2019/11/relstorage-30.html#performance-improvements>`_
 for details.
 
 RelStorage 2.1a1 vs RelStorage 2.0