Refactor: Use 'source' variable consistently in log formatting

Author: minwoo1999

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/java/SimpleFormatter.java

@@ -45,8 +45,8 @@ public String format(LogRecord record) {
 		String message = formatMessage(record);
 		String throwable = getThrowable(record);
 		String thread = getThreadName();
-		return String.format(this.format, date, source, record.getLoggerName(), record.getLevel().getLocalizedName(),
-				message, throwable, thread, this.pid);
+		return String.format(this.format, date, source, source, record.getLevel().getLocalizedName(), message,
+				throwable, thread, this.pid);
 	}
 
 	private String getThrowable(LogRecord record) {