client test failures

[QuChen88]

I noticed a few memcache-client test cases fail when I run npm test locally. I don't think this is a functional bug as the client works fine. This is most likely a test issue which would be nice to fix.

FAIL  src/test/spec/client.spec.ts (7.634 s) (10 failures)
  memcache client
    ✕ should not get system ETIMEDOUT error after custom connect timeout (2 ms)
    ✕ should set and get multiple keys concurrently with 1 maxConnections (14 ms)
    ✕ should set and get multiple keys concurrently with 2 maxConnections (11 ms)
    ✕ should set and get multiple keys concurrently with 3 maxConnections (7 ms)
    ✕ should set and get multiple keys concurrently with 4 maxConnections (7 ms)
    ✕ should set and get multiple keys concurrently with 5 maxConnections (5 ms)
    ✕ should set and get multiple keys concurrently with 10 maxConnections (3 ms)
    ✕ should handle error if can't JSON.stringify value (6 ms)
    ✕ should gracefully propagate decompress error (5002 ms)
    ✕ should handle command timeout error (105 ms)