Update slf4j-api dependency to 1.7.18

Author: lukespragg

build.gradle

@@ -58,7 +58,7 @@ repositories {
 // Project dependencies
 dependencies {
     compile 'io.netty:netty-all:4.0.33.Final'
-    compile 'org.slf4j:slf4j-api:1.7.13'
+    compile 'org.slf4j:slf4j-api:1.7.18'
     testCompile 'junit:junit:4.12'
     testCompile 'org.hamcrest:hamcrest-library:1.3'
     testCompile 'org.powermock:powermock-api-mockito:1.6.4'

pom.xml

@@ -98,7 +98,7 @@
         <dependency>
             <groupId>org.slf4j</groupId>
             <artifactId>slf4j-api</artifactId>
-            <version>1.7.13</version>
+            <version>1.7.18</version>
             <scope>compile</scope>
         </dependency>
         <!-- Testing only -->