Update ID of first background job

The job ID of the first background job is now 1, this reflects PIDs a
bit better, so one can refer to the main thread as being job 0.

Author: cosineblast

crates/nu-protocol/src/engine/jobs.rs

@@ -9,13 +9,22 @@ use crate::Signals;
 
 use super::JobId;
 
-#[derive(Default)]
 pub struct Jobs {
     next_job_id: JobId,
     last_frozen_job_id: Option<JobId>,
     jobs: HashMap<JobId, Job>,
 }
 
+impl Default for Jobs {
+    fn default() -> Self {
+        Self {
+            next_job_id: 1,
+            last_frozen_job_id: None,
+            jobs: HashMap::default()
+        }
+    }
+}
+
 impl Jobs {
     pub fn iter(&self) -> impl Iterator<Item = (JobId, &Job)> {
         self.jobs.iter().map(|(k, v)| (*k, v))