Use <kbd> tag for keyboard shortcuts

src/ch17-02-concurrency-with-async.md

@@ -274,7 +274,7 @@ there are still a couple of problems. For one thing, the messages do not arrive
 at half-second intervals. They arrive all at once, 2 seconds (2,000
 milliseconds) after we start the program. For another, this program never exits!
 Instead, it waits forever for new messages. You will need to shut it down using
-<span class="keystroke">ctrl-c</span>.
+<kbd>ctrl</kbd>-<kbd>c</kbd>.
 
 Let’s start by examining why the messages come in all at once after the full
 delay, rather than coming in with delays between each one. Within a given async

src/ch17-04-streams.md

@@ -345,8 +345,8 @@ which is longer than the other durations we are using. Here, we create a
 through the stream, and pin it so that it’s safe to do so. That gets us _almost_
 to where we need to be. Everything type checks. If you run this, though, there
 will be two problems. First, it will never stop! You’ll need to stop it with
-<span class="keystroke">ctrl-c</span>. Second, the messages from the English
-alphabet will be buried in the midst of all the interval counter messages:
+<kbd>ctrl</kbd>-<kbd>c</kbd>. Second, the messages from the English alphabet
+will be buried in the midst of all the interval counter messages:
 
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