translator: handle new pathlib usage in sphinx-env

Sphinx environment's `doc2path` call now returns a Path [1]; updating
the source-link logic to handle a string conversion before extracting
the suffix.

[1]: sphinx-doc/sphinx@de15d61

Signed-off-by: James Knight <[email protected]>
(cherry picked from commit 4da8461)

Author: jdknight

sphinxcontrib/confluencebuilder/storage/translator.py

@@ -2560,7 +2560,8 @@ def visit_confluence_source_link(self, node):
         uri = PARAMS(node)['url']
 
         docname = self.docname
-        suffix = self.builder.env.doc2path(docname, base=None)[len(docname):]
+        docpath = str(self.builder.env.doc2path(docname, base=None))
+        suffix = docpath[len(docname):]
         uri = uri.format(page=docname, suffix=suffix, **PARAMS(node))
 
         source_text = PARAMS(node).get('text', L('Edit Source'))