Update github leaderboard link with the new one

[anjula-sack]

Is your feature request related to a problem? Please describe.

• We need to update the GitHub leaderboard link

Describe the solution you'd like

• Replace https://sef-github-leaderboard.herokuapp.com/ with https://wehuddle.sefglobal.org/leaderboard

Are you working on it? No

[anjula-sack]

@dilankavishka can you work on this?

[dilankavishka]

@anjula-sack sure