Upgrade to Logback 1.1.8

Closes gh-7638

spring-boot-dependencies/pom.xml

@@ -124,7 +124,7 @@
 		<junit.version>4.12</junit.version>
 		<liquibase.version>3.5.3</liquibase.version>
 		<log4j2.version>2.6.2</log4j2.version>
-		<logback.version>1.1.7</logback.version>
+		<logback.version>1.1.8</logback.version>
 		<lombok.version>1.16.10</lombok.version>
 		<mariadb.version>1.4.6</mariadb.version>
 		<mockito.version>1.10.19</mockito.version>

spring-boot/src/main/java/org/springframework/boot/logging/logback/DefaultLogbackConfiguration.java

 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -26,6 +26,7 @@ import ch.qos.logback.core.ConsoleAppender;
 import ch.qos.logback.core.rolling.FixedWindowRollingPolicy;
 import ch.qos.logback.core.rolling.RollingFileAppender;
 import ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy;
+import ch.qos.logback.core.util.FileSize;
 import ch.qos.logback.core.util.OptionHelper;
 
 import org.springframework.boot.bind.RelaxedPropertyResolver;
@@ -142,7 +143,7 @@ class DefaultLogbackConfiguration {
 		config.start(rollingPolicy);
 
 		SizeBasedTriggeringPolicy<ILoggingEvent> triggeringPolicy = new SizeBasedTriggeringPolicy<ILoggingEvent>();
-		triggeringPolicy.setMaxFileSize("10MB");
+		triggeringPolicy.setMaxFileSize(FileSize.valueOf("10MB"));
 		appender.setTriggeringPolicy(triggeringPolicy);
 		config.start(triggeringPolicy);