[PubSub] Phpdoc for PubSubClient's constructor is incorrect

[taka-oyama]

I noticed that

google-cloud-php/PubSub/src/PubSubClient.php

Lines 146 to 147 in 4021aec

	* @type CacheItemPoolInterface $authCache A cache for storing access
	* tokens. **Defaults to** a simple in memory implementation.

Doesn't work. It's suppose to be credentials.authCache.
I think the same thing can be said for authCacheOptions.

I'm fairly certain keyFilePath doesn't work here either.

Please take a look. Thanks.

[taka-oyama]

I found a migration page that describes the changes. I guess someone forgot to update the phpdoc?

70e2265#diff-7e7a3f0069164da412cef8834788fd94cabb3d11bdd2ee31cd996bd7e23fa5f7R17-R39