Upgrade to slf4j 1.7.12

Release notes:

http://www.slf4j.org/news.html

pom.xml

@@ -319,7 +319,7 @@
     <dependency>
       <groupId>org.slf4j</groupId>
       <artifactId>slf4j-api</artifactId>
-      <version>1.7.10</version>
+      <version>1.7.12</version>
     </dependency>
   </dependencies>
 </project>