Added Redis retry_strategy

Most of the ClientOpts that have to do with reconnecting have been
deprecated in favor of the `retry_strategy` property. The
DefinitelyTyped repo is outdated and is missing the retry_strategy
property. See the docs at https://github.com/NodeRedis/node_redis.

The following options of ClientOpts are deprecated in favor of
retry_strategy:
- retry_max_delay
- connect_timeout
- max_attempts

redis/redis.d.ts

@@ -34,6 +34,10 @@ declare module "redis" {
         versions: number[];
     }
 
+    interface RetryStrategy {
+      (options: {error: Error, total_retry_time: number, times_connected: number, attempt: number}): number;
+    }
+
     export interface ClientOpts {
         parser?: string;
         return_buffers?: boolean;
@@ -50,6 +54,7 @@ declare module "redis" {
         family?: string;
         command_queue_high_water?: number;
         command_queue_low_water?: number;
+        retry_strategy?: RetryStrategy;
     }
 
     export interface RedisClient extends NodeJS.EventEmitter {