Merge pull request #301 from zoj613/list_prefix

Fix error in the v3 spec regarding discovering all nodes using `list_prefix`.

Author: joshmoore

docs/v3/core/v3.0.rst

@@ -1549,7 +1549,7 @@ Let "+" be the string concatenation operator.
     groups.
 
     For hierarchies without group storage transformers one may also call
-    ``list_prefix("/")``. All ``zarr.json`` keys represent either explicit
+    ``list_prefix("")``. All ``zarr.json`` keys represent either explicit
     groups or arrays. All intermediate prefixes ending in a ``/`` are implicit
     groups.