Update Piston to fix bugs

Closes #1292 via Piston fixes.

(cherry picked from commit dc56b602c0367fbd24f954de2b8be4e864add59f)

worldedit-core/src/main/java/com/sk89q/worldedit/command/argument/AbstractDirectionConverter.java

@@ -111,7 +111,7 @@ public abstract class AbstractDirectionConverter<D> implements ArgumentConverter
     }
 
     @Override
-    public List<String> getSuggestions(String input) {
+    public List<String> getSuggestions(String input, InjectedValueAccess context) {
         return limitByPrefix(suggestions.stream(), input);
     }
 

worldedit-core/src/main/java/com/sk89q/worldedit/command/argument/CommaSeparatedValuesConverter.java

@@ -70,9 +70,10 @@ public class CommaSeparatedValuesConverter<T> implements ArgumentConverter<T> {
     }
 
     @Override
-    public List<String> getSuggestions(String input) {
+    public List<String> getSuggestions(String input, InjectedValueAccess context) {
         String lastInput = Iterables.getLast(COMMA.split(input), "");
-        return delegate.getSuggestions(lastInput);
+        assert lastInput != null;
+        return delegate.getSuggestions(lastInput, context);
     }
 
     @Override

worldedit-core/src/main/java/com/sk89q/worldedit/command/argument/EntityRemoverConverter.java

@@ -55,7 +55,7 @@ public class EntityRemoverConverter implements ArgumentConverter<EntityRemover>
     }
 
     @Override
-    public List<String> getSuggestions(String input) {
+    public List<String> getSuggestions(String input, InjectedValueAccess context) {
         return limitByPrefix(suggestions.stream(), input);
     }
 

worldedit-core/src/main/java/com/sk89q/worldedit/command/argument/FactoryConverter.java

@@ -133,7 +133,7 @@ public class FactoryConverter<T> implements ArgumentConverter<T> {
     }
 
     @Override
-    public List<String> getSuggestions(String input) {
+    public List<String> getSuggestions(String input, InjectedValueAccess context) {
         return factoryExtractor.apply(worldEdit).getSuggestions(input);
     }
 

worldedit-core/src/main/java/com/sk89q/worldedit/command/argument/RegistryConverter.java

@@ -104,7 +104,8 @@ public final class RegistryConverter<V extends Keyed> implements ArgumentConvert
                 : SuccessfulConversion.fromSingle(result);
     }
 
-    public List<String> getSuggestions(String input) {
+    @Override
+    public List<String> getSuggestions(String input, InjectedValueAccess context) {
         return SuggestionHelper.getRegistrySuggestions(registry, input).collect(Collectors.toList());
     }
 }

worldedit-core/src/main/java/com/sk89q/worldedit/command/argument/WorldConverter.java

@@ -61,7 +61,7 @@ public class WorldConverter implements ArgumentConverter<World> {
     }
 
     @Override
-    public List<String> getSuggestions(String input) {
+    public List<String> getSuggestions(String input, InjectedValueAccess context) {
         return getWorlds()
                 .map(World::getId)
                 .filter(world -> world.startsWith(input))