Fix resurrect timeout formula (#833)

* Fixes #827

* Updated test

lib/ConnectionPool.js

@@ -34,11 +34,7 @@ class ConnectionPool {
     this._ssl = opts.ssl
     this._agent = opts.agent
     // the resurrect timeout is 60s
-    // we multiply it by 2 because the resurrect formula is
-    // `Math.pow(resurrectTimeout * 2, deadCount -1)`
-    // and we don't need to multiply by 2
-    // the resurrectTimeout every time
-    this.resurrectTimeout = 1000 * 60 * 2
+    this.resurrectTimeout = 1000 * 60
     // number of consecutive failures after which
     // the timeout doesn't increase
     this.resurrectTimeoutCutoff = 5
@@ -94,15 +90,9 @@ class ConnectionPool {
     connection.status = Connection.statuses.DEAD
     connection.deadCount++
     // resurrectTimeout formula:
-    // `Math.pow(resurrectTimeout * 2, deadCount -1)`
-    // we don't need to multiply the resurrectTimeout by 2
-    // every time, it is cached during the initialization
-    connection.resurrectTimeout = Date.now() + Math.pow(
-      this.resurrectTimeout,
-      Math.min(
-        connection.deadCount - 1,
-        this.resurrectTimeoutCutoff
-      )
+    // `resurrectTimeout * 2 ** min(deadCount - 1, resurrectTimeoutCutoff)`
+    connection.resurrectTimeout = Date.now() + this.resurrectTimeout * Math.pow(
+      2, Math.min(connection.deadCount - 1, this.resurrectTimeoutCutoff)
     )
 
     // sort the dead list in ascending order