commands: document the "common" class attribute

Switch it to uppercase to make it clear it's a constant, and add
documentation so its usage is clear.

Change-Id: I6d281a66a90b5908b3131585c9945e88cfe815ea
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/309322
Reviewed-by: Raman Tenneti <rtenneti@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/subcmds/download.py b/subcmds/download.py
index 81d997e0..523f25e0 100644
--- a/subcmds/download.py
+++ b/subcmds/download.py
@@ -22,7 +22,7 @@ CHANGE_RE = re.compile(r'^([1-9][0-9]*)(?:[/\.-]([1-9][0-9]*))?$')
 
 
 class Download(Command):
-  common = True
+  COMMON = True
   helpSummary = "Download and checkout a change"
   helpUsage = """
 %prog {[project] change[/patchset]}...