Correct number of proposals students can submit

[ojwb]

It's now 3 not 5.

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[ojwb]

Is a CLA really necessary for a single character change? This seems to be adding unnecessary friction to the process.

My personal policy is not to sign CLAs so if a CLA is a hard requirement I guess just close this PR.

[rspier]

The short answer is yes: A CLA is required to commit to this repo.

I used grep to find the offending 5, and have pushed an equivalent change.