[fix] Fix comment for ConnectionMaxIdleTime

[massakam]

Motivation

The default value of ConnectionMaxIdleTime is said to be 60 seconds in the comment,

pulsar-client-go/pulsar/client.go

Lines 155 to 157 in 2a15a25

	// Release the connection if it is not used for more than ConnectionMaxIdleTime.
	// Default is 60 seconds, negative such as -1 to disable.
	ConnectionMaxIdleTime time.Duration

but it actually seems to be 180 seconds. 60 seconds is the minimum value, not the default value.

pulsar-client-go/pulsar/client_impl.go

Lines 39 to 40 in 2a15a25

	defaultConnMaxIdleTime = 180 * time.Second
	minConnMaxIdleTime = 60 * time.Second

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