Remove StringUtils#join in favor of String#join (Java 8)

src/test/java/tools/checktestmocks/CheckTestMocks.java

@@ -1,10 +1,8 @@
 package tools.checktestmocks;
 
-import com.google.common.collect.Collections2;
 import com.google.common.collect.Sets;
 import fr.xephi.authme.ClassCollector;
 import fr.xephi.authme.TestHelper;
-import fr.xephi.authme.util.StringUtils;
 import org.mockito.Mock;
 import tools.utils.AutoToolTask;
 import tools.utils.InjectorUtils;
@@ -16,6 +14,7 @@ import java.util.HashSet;
 import java.util.List;
 import java.util.Scanner;
 import java.util.Set;
+import java.util.stream.Collectors;
 
 /**
  * Task checking if all tests' {@code @Mock} fields have a corresponding
@@ -41,7 +40,7 @@ public class CheckTestMocks implements AutoToolTask {
         for (Class<?> clazz : collector.collectClasses(c -> isTestClassWithMocks(c))) {
             checkClass(clazz);
         }
-        System.out.println(StringUtils.join("\n", errors));
+        System.out.println(String.join("\n", errors));
     }
 
     /**
@@ -112,8 +111,9 @@ public class CheckTestMocks implements AutoToolTask {
     }
 
     private static String formatClassList(Collection<Class<?>> coll) {
-        Collection<String> classNames = Collections2.transform(coll, Class::getSimpleName);
-        return StringUtils.join(", ", classNames);
+        return coll.stream()
+            .map(Class::getSimpleName)
+            .collect(Collectors.joining(", "));
     }
 
 }

src/test/java/tools/messages/translation/MessageExport.java

@@ -1,7 +1,5 @@
 package tools.messages.translation;
 
-import fr.xephi.authme.util.StringUtils;
-
 /**
  * Container class for one translatable message.
  */
@@ -14,7 +12,7 @@ public class MessageExport {
 
     public MessageExport(String key, String[] tags, String defaultMessage, String translatedMessage) {
         this.key = key;
-        this.tags = StringUtils.join(",", tags);
+        this.tags = String.join(",", tags);
         this.defaultMessage = defaultMessage;
         this.translatedMessage = translatedMessage;
     }