Fixed confusion between float and int in docs

[simone1999]

Both the Solana token standard and ERC20 use integers to store token amounts, not floats. The given calculation for the maximum amount a Solana token can reach already is correctly based on an uint64, not an ufloat64.

[simone1999]

It's a very small change, but as a float can reach many orders of magnitude higher values than an int, better to correct it and avoid confusion.