--help doesn't display correctly when using sub-groups;

Hey, great job, love the tool !!!!

When creating command groups using classes, --help isn't correctly displaying.

**Consider this example**

```
import fire
class GroupBase:
def __init__(self, verbose: bool):
self.verbose = verbose
class Group1(GroupBase):
def command1(self):
"""This command seen by group 1 only"""
print(f"I am a group1 command with verbosity {self.verbose}")
class Group2(GroupBase):
def command2(self):
"""This command will be seen by group 2."""
print(f"I am a group2 command with verbosity {self.verbose}")
class Base:
def __init__(self, verbose: bool = False):
self.verbose = verbose
self.group1 = Group1(verbose)
self.group2 = Group2(verbose)
def common1(self):
"""This command will be seen at the base level."""
print(f"I am a common command with verbosity {self.verbose}")
def main():
fire.Fire(Base)
if __name__ == '__main__':
main()
```

**if I type `python main.py`, I get the correct help file; Note the existence of the two groups (group1, group2).** (though help for verbose isn't correct.)

```
NAME
main.py

SYNOPSIS
main.py - GROUP | COMMAND | VALUE

GROUPS
GROUP is one of the following:

group1

group2

COMMANDS
COMMAND is one of the following:

common1
This command will be seen at the base level.

VALUES
VALUE is one of the following:

verbose
```

**If, instead, I use --help `python main.py --help`**, groups are not shown.

```
NAME
main.py

SYNOPSIS
main.py

FLAGS
--verbose=VERBOSE
Type: bool
Default: False
```