Fix comment inclusion not working on python-protobuf 3.0 (#85, #645)

The old python-protobuf library didn't have __str__() handler for
repeated fields, so have to convert to list() first.
diff --git a/generator/nanopb_generator.py b/generator/nanopb_generator.py
index cc4ed40..578deb7 100755
--- a/generator/nanopb_generator.py
+++ b/generator/nanopb_generator.py
@@ -1615,11 +1615,10 @@
         # process source code comment locations
         # ignores any locations that do not contain any comment information
         self.comment_locations = {
-            str(location.path): location
+            str(list(location.path)): location
             for location in self.fdesc.source_code_info.location
             if location.leading_comments or location.leading_detached_comments or location.trailing_comments
         }
-        # breakpoint()
 
         for index, enum in enumerate(self.fdesc.enum_type):
             name = create_name(enum.name)