Fixed a typo, changed timeout_ms cancellation time to be < 0

[BobbedBob]

修复拼写错误，更改timer_function中取消计时器的条件为小于零。
更改为小于零-1还可以正常使用，而且若timeout是-1一之外的负数，程序不会报错。
Fixed a typo, changed timeout_ms cancellation time to be < 0.
-1 can still be used normally, and if timeout is a negative number is -1, the program will not throw an exception.

[lexiforest]

Do you have any link to the documentation or code example that explains why timeout can be a negative number other than -1.

[BobbedBob]

No, but it is possible to pass such an argument to the function, and it can act as a safeguard for when that happens if there's some sort of error with calculations.

[lexiforest]

I don't think that there will be any other negative values passed to this callback function. Unless there is bug in the libcurl implementation, I think we should adhere to what the libcurl doc says:

A timeout_ms value of -1 passed to this callback means you should delete the timer. All other values are valid expire times in number of milliseconds.

If you want to fix the typo, please open a separate PR.