Correct syntax for thread name formatting in Logback XML configuration

See gh-2366

spring-boot/src/main/resources/org/springframework/boot/logging/logback/basic.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <included>
-	<property name="CONSOLE_LOG_PATTERN" value="%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){faint} %clr(%5p) %clr(${PID:- }){magenta} %clr(---){faint} %clr([%15.15t{14}]){faint} %clr(%-40.40logger{39}){cyan} %clr(:){faint} %m%n%wex"/>
+	<property name="CONSOLE_LOG_PATTERN" value="%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){faint} %clr(%5p) %clr(${PID:- }){magenta} %clr(---){faint} %clr([%15.15t]){faint} %clr(%-40.40logger{39}){cyan} %clr(:){faint} %m%n%wex"/>
 
 	<conversionRule conversionWord="clr" converterClass="org.springframework.boot.logging.logback.ColorConverter" />
 	<conversionRule conversionWord="wex" converterClass="org.springframework.boot.logging.logback.WhitespaceThrowableProxyConverter" />