Update account_put_deploy example to work with current casper-node

[jacek-casper]

What does this PR fix/introduce?

It changes the account_put_deploy example slightly to pass validation on the current dev version of casper-node.

Additional context

When on-boarding I was trying it examples in the docs and I noticed a few issues:

• the amount in the example is I32, but that seems to be disallowed in casper-node, leading to an error failed to parse transfer 'amount' as U512
• the Transfer object doesn't have a target, which is currently also rejected in casper-node: missing transfer 'target' runtime argument
• casper-node currently enforces a minimal transfer amount of 2500000000, so I've set the amount to that as well

Checklist

(Delete any that aren't relevant)

• Docs are successfully building - yarn install && yarn run build.

Reviewers

[ACStone-MTS]

Looks good to me!