Post-release version bump

src/libostree/libostree-devel.sym

@@ -17,6 +17,13 @@
   Boston, MA 02111-1307, USA.
 ***/
 
+LIBOSTREE_2020.5 {
+global:
+  /* Add symbols here, and uncomment the bits in
+   * Makefile-libostree.am to enable this too.
+   */
+} LIBOSTREE_2020.4;
+
 /* Stub section for the stable release *after* this development one; don't
  * edit this other than to update the year.  This is just a copy/paste
  * source.  Replace $LASTSTABLE with the last stable version, and $NEWVERSION