Add UTF-8 charset element to logback base.xml

Update base logback configuration to include a UTF-8 charset element
which helps with multilanguage support.

Fixes gh-1618

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

@@ -8,6 +8,7 @@
 	<appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
 		<encoder>
 			<pattern>${CONSOLE_LOG_PATTERN}</pattern>
+			<charset>utf-8</charset>
 		</encoder>
 	</appender>