Make a few classes final

src/main/java/de/prob2/jupyter/Main.java

@@ -15,7 +15,7 @@ import com.google.inject.Stage;
 import io.github.spencerpark.jupyter.channels.JupyterConnection;
 import io.github.spencerpark.jupyter.kernel.KernelConnectionProperties;
 
-public class Main {
+public final class Main {
 	private Main() {
 		super();
 		

src/main/java/de/prob2/jupyter/ProBKernel.java

@@ -27,7 +27,7 @@ import io.github.spencerpark.jupyter.messages.DisplayData;
 
 import org.jetbrains.annotations.NotNull;
 
-public class ProBKernel extends BaseKernel {
+public final class ProBKernel extends BaseKernel {
 	private static final Pattern COMMAND_PATTERN = Pattern.compile("\\s*\\:(.*)");
 	
 	private final @NotNull Map<@NotNull String, @NotNull ReplCommand> commands;

src/main/java/de/prob2/jupyter/ProBKernelModule.java

@@ -4,7 +4,7 @@ import com.google.inject.AbstractModule;
 
 import de.prob.MainModule;
 
-public class ProBKernelModule extends AbstractModule {
+public final class ProBKernelModule extends AbstractModule {
 	@Override
 	protected void configure() {
 		install(new MainModule());