Round ttl to integer ms

Fixes #35

index.js

@@ -380,7 +380,8 @@ module.exports = class CachePolicy {
     }
 
     /**
-     * Value of applicable max-age (or heuristic equivalent) in seconds. This counts since response's `Date`.
+     * Possibly outdated value of applicable max-age (or heuristic equivalent) in seconds.
+     * This counts since response's `Date`.
      *
      * For an up-to-date value, see `timeToLive()`.
      *
@@ -446,11 +447,16 @@ module.exports = class CachePolicy {
         return defaultMinTtl;
     }
 
+    /**
+     * Up-to-date `max-age` value, in *milliseconds*.
+     *
+     * Prefer this method over `maxAge()`.
+     */
     timeToLive() {
         const age = this.maxAge() - this.age();
         const staleIfErrorAge = age + toNumberOrZero(this._rescc['stale-if-error']);
         const staleWhileRevalidateAge = age + toNumberOrZero(this._rescc['stale-while-revalidate']);
-        return Math.max(0, age, staleIfErrorAge, staleWhileRevalidateAge) * 1000;
+        return Math.round(Math.max(0, age, staleIfErrorAge, staleWhileRevalidateAge) * 1000);
     }
 
     stale() {