docs: LogFormatter: $plaintext and $irctext are booleans

It seems all references to them assume the values as booleans.
Code search: https://codesearch.wmcloud.org/deployed/?q=%5C%24this-%3E(plaintext%7Circtext)&i=nope&files=LogFormatter(test)%3F%5C.php&excludeFiles=&repos=

Change-Id: I9bde1f7b1cac0ba9c0b002fd1b57a4407a4912ce

includes/logging/LogFormatter.php

@@ -94,11 +94,11 @@ class LogFormatter {
 	 * be included in page history or send to IRC feed. Links are replaced
 	 * with plaintext or with [[pagename]] kind of syntax, that is parsed
 	 * by page histories and IRC feeds.
-	 * @var string
+	 * @var bool
 	 */
 	protected $plaintext = false;
 
-	/** @var string */
+	/** @var bool */
 	protected $irctext = false;
 
 	/**