Update lexeu-competition.md

[ANDROIDHASSAN]

I have corrected the spelling of gather in the documentation

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

• this was a docs update i have corrected the typos like gathe in gather

• Why was this change needed? (You can also link to an open issue here)
  it's a typo and this is wrong

• Other information:

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[dartpain]

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