Add slf4j-log4j12 dependency

Fixes the "Failed to load class org.slf4j.impl.StaticLoggerBinder" message
when building.

Author: dr0i

metafix/build.gradle

@@ -20,6 +20,7 @@ dependencies {
   implementation "org.eclipse.xtext:org.eclipse.xtext:${versions.xtext}"
   implementation "org.eclipse.xtext:org.eclipse.xtext.xbase:${versions.xtext}"
   implementation "org.slf4j:slf4j-api:${versions.slf4j}"
+  implementation "org.slf4j:slf4j-log4j12:${versions.slf4j}"
 
   testImplementation "org.junit.jupiter:junit-jupiter-api:${versions.junit_jupiter}"
   testImplementation "org.junit.platform:junit-platform-launcher:${versions.junit_platform}"