Apply prefer-const lint rule

lib/scheduling.js

@@ -44,7 +44,7 @@ function interval(timestamp, intrvl, offset = 0) {
 }
 
 function parseCron(cronExp) {
-  let parts = cronExp.trim().split(/\s+/);
+  const parts = cronExp.trim().split(/\s+/);
   if (parts.length === 5) parts.unshift("*");
 
   return later.schedule(later.parse.cron(parts.join(" "), true));
@@ -54,10 +54,10 @@ function cron(timestamp, schedule, offset = 0) {
   // TODO later.js doesn't throw erorr if expression is invalid!
   const ret = [0, 0];
 
-  let prev = schedule.prev(1, new Date(timestamp + offset));
+  const prev = schedule.prev(1, new Date(timestamp + offset));
   if (prev) ret[0] = prev.setMilliseconds(0) - offset;
 
-  let next = schedule.next(1, new Date(timestamp + offset + 1000));
+  const next = schedule.next(1, new Date(timestamp + offset + 1000));
   if (next) ret[1] = next.setMilliseconds(0) - offset;
 
   return ret;