Upgrade to SLF4J 1.7.13

Closes gh-4717

Author: wilkinsona

spring-boot-dependencies/pom.xml

@@ -107,7 +107,7 @@
 		<reactor-spring.version>1.1.3.RELEASE</reactor-spring.version>
 		<servlet-api.version>3.1.0</servlet-api.version>
 		<simple-json.version>1.1.1</simple-json.version>
-		<slf4j.version>1.7.12</slf4j.version>
+		<slf4j.version>1.7.13</slf4j.version>
 		<snakeyaml.version>1.14</snakeyaml.version>
 		<solr.version>4.7.2</solr.version>
 		<spock.version>0.7-groovy-2.0</spock.version>