Remove 'in seconds' from the docs for SetKeepAlive and SetPingTimeout

At some point in the past these functions probably did take ints and assumed those
values would relate to the number of seconds for these features. They were changed
to take a time.Duration but the docs were not updated.

resolves eclipse-paho#152

options.go

@@ -177,7 +177,7 @@ func (o *ClientOptions) SetStore(s Store) *ClientOptions {
 	return o
 }
 
-// SetKeepAlive will set the amount of time (in seconds) that the client
+// SetKeepAlive will set the amount of time that the client
 // should wait before sending a PING request to the broker. This will
 // allow the client to know that a connection has not been lost with the
 // server.
@@ -186,7 +186,7 @@ func (o *ClientOptions) SetKeepAlive(k time.Duration) *ClientOptions {
 	return o
 }
 
-// SetPingTimeout will set the amount of time (in seconds) that the client
+// SetPingTimeout will set the amount of time that the client
 // will wait after sending a PING request to the broker, before deciding
 // that the connection has been lost. Default is 10 seconds.
 func (o *ClientOptions) SetPingTimeout(k time.Duration) *ClientOptions {