Fix issue with is_some.

[mikemadden42]

This fixes an issue in the falcon_host_details example.

   Compiling rusty_falcon v0.4.0 (/Users/mmadden/src/rusty-falcon)
error[E0599]: no method named `is_some` found for struct `Vec<MsaspecPeriodError>` in the current scope
  --> examples/falcon_host_details.rs:54:24
   |
54 |     if response.errors.is_some() {
   |                        ^^^^^^^
   |
help: there is a method `is_sorted` with a similar name
   |
54 |     if response.errors.is_sorted() {
   |                        ~~~~~~~~~