Strengthen `elemSmallerThanBound`
Strengthen `elemSmallerThanBound`

For a `n : Fin m`, we have `n < m`,
whereas `elemSmallerThanBound` only proves `n <= m`,
even though the name and the docstring suggest otherwise.

kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev