Use real ‘def’, not ‘lambda’, to define next()

logging_tree/format.py

@@ -4,8 +4,8 @@
 import sys
 
 if sys.version_info < (2, 6):
-    next = lambda generator: generator.next()  # supply a missing builtin
-
+    def next(generator):
+        return generator.next()
 
 def printout(node=None):
     """Print a tree of loggers, given a `Node` from `logging_tree.nodes`.