Upgrade to Log4j 2 2.1

Closes gh-1889

spring-boot-dependencies/pom.xml

@@ -94,7 +94,7 @@
 		<junit.version>4.11</junit.version>
 		<liquibase.version>3.3.0</liquibase.version>
 		<log4j.version>1.2.17</log4j.version>
-		<log4j2.version>2.0.2</log4j2.version>
+		<log4j2.version>2.1</log4j2.version>
 		<logback.version>1.1.2</logback.version>
 		<mockito.version>1.9.5</mockito.version>
 		<mongodb.version>2.12.4</mongodb.version>