export dbname/1

BugzID: 45853

This is a cherry-pick of:

https://github.com/cloudant/fabric/commit/818dd09e9ea645e866fc62fd1a4302ce73b2422a
diff --git a/src/fabric.erl b/src/fabric.erl
index 26b9f62..c3a95fb 100644
--- a/src/fabric.erl
+++ b/src/fabric.erl
@@ -33,7 +33,7 @@
 
 % miscellany
 -export([design_docs/1, reset_validation_funs/1, cleanup_index_files/0,
-    cleanup_index_files/1]).
+    cleanup_index_files/1, dbname/1]).
 
 -include_lib("fabric/include/fabric.hrl").