double type has incorrect PLAIN representation for infinity values

[nmiyake]

What happened?

• Create a Conjure definition that sends a double value using PLAIN serialization (for example, specify an endpoint with a query parameter of type double) and send a double with the value of negative or positive infinity
• The value is sent as +Inf or -Inf

What did you want to happen?

Per https://github.com/palantir/conjure/blob/master/docs/spec/wire.md#6-plain-format, the value should be sent as +Infinity/-Infinity