fix(schema.mustache): table down() function comment

[un-versed]

changed "alternations" to "alterations"

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• [x] Bugfix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
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[coveralls]

Coverage remained the same at 48.438% when pulling 3b78196992b2254f1c6b2ab5b68ff9c59f00627c on un-versed:patch-1 into 1e698919332d65e629b73a0ea8a800274e9e1cf1 on adonisjs:develop.