Simple hello world snap is not working after upgrade ubuntu 18.04 to 20.04

Recently, I have started working on snapping. I have learnt snapping on Ubuntu 18.04 with simple hello-gnu.

After that i have moved to ubuntu 20.04. I have faced many issue. So i decided to simply run hello-gnu snap again on ubuntu 20.04. But it’s failing with below error

Launching a VM.,    
snap "snapd" has no updates available                                               
core18 20201210 from Canonical✓ installed    
"core18" switched to the "latest/stable" channel    
snapd is not logged in, snap install commands will use sudo snap "core20" has no updates available    
Skipping pull hello-world (already ran)    
Skipping build hello-world (already ran)    
Skipping stage hello-world (already ran)    
Skipping prime hello-world (already ran)    
Failed to generate snap metadata: The specified command 'bin/hello' defined in the app 'hello' does not exist.    
Ensure that 'bin/hello' is installed with the correct path.    
Run the same command again with --debug to shell into the environment if you wish to introspect this failure.

snapcraft.yaml is look like as below

name: hello-gnu # you probably want to 'snapcraft register <name>'
base: core20 # the base snap is the execution environment for this snap
version: '0.1' # just for humans, typically '1.2+git' or '1.3.2'
summary: Hello simple snap
description: |
  This is my-snap's description. You have a paragraph or two to tell the
  most important story about your snap. Keep it under 100 words though,
  we live in tweetspace and your description wants to look good in the snap

grade: devel # must be 'stable' to release into candidate/stable channels
confinement: devmode # use 'strict' once you have the right plugs and slots

    command: bin/hello

    # See 'snapcraft plugins'
    plugin: autotools