examples: Minor fix in routeguide example

[arjan-bal]

Motivation

1. The following logs line prints a feature but the logs mentions NOTE. NOTE messages are printed later in bidirectional stream code, so this may be a copy/paste error.

println!("NOTE = {:?}", feature);

2. The following line in the markdown file declares tx as mut which and detected by rust-analyzer. The actual client file doesn't declare tx as mut.

let (mut tx, rx) = mpsc::channel(4);

Client code:

tonic/examples/src/routeguide/server.rs

Lines 47 to 48 in a7030a7

	let (tx, rx) = mpsc::channel(4);
	let features = self.features.clone();

Solution

1. Make the print statement accurate.
2. Remove the unnecessary mut.

[tottoto]

Thanks.