Call attention to call button via primary class

Signed-off-by: Jan-Christoph Borchardt <hey@jancborchardt.net>

js/views/callinfoview.js

@@ -38,11 +38,11 @@
 		'{{/if}}' +
 		'{{#if participantInCall}}' +
 		'	<div>' +
-		'		<button class="leave-call">' + t('spreed', 'Leave call') + '</button>' +
+		'		<button class="leave-call primary">' + t('spreed', 'Leave call') + '</button>' +
 		'	</div>' +
 		'{{else}}' +
 		'	<div>' +
-		'		<button class="join-call">' + t('spreed', 'Join call') + '</button>' +
+		'		<button class="join-call primary">' + t('spreed', 'Join call') + '</button>' +
 		'	</div>' +
 		'{{/if}}' +
 		'{{#if canModerate}}' +