[BUG] ExpCog sends Level Up message when user hasn't levelled up

[rosalogia]

Describe the bug
Sometimes upon GitHub events, users who are registered with the GitHubCog get Level Up messages from the ExpCog in the project-updates channel even if they have not gained enough experience to level up. When the user has gained enough experience to level up, the message is not shown. It is unclear why this is

To Reproduce
Steps to reproduce the behavior:

1. Register user's GitHub with !register
2. Have user gain a certain amount of experience from repository contributions
3. Wait for Level Up message to eventually be sent

Expected behavior
Level Up messages should be sent when the user gains enough experience to level up.

Screenshots