Fix warning

src/compiler.rs

@@ -272,7 +272,7 @@ impl StmtVisitor<()> for Compiler {
 		self.emit_opcode(OpCode::Ret);
 	}
 
-	fn visit_binary_assign_stmt(&mut self, stmt: &BinaryAssignStmt, _: usize) -> () {
+	fn visit_binary_assign_stmt(&mut self, stmt: &BinaryAssignStmt, _: usize) {
 		let var_id = self.get_variable(stmt.name.clone());
 		self.emit_opcode(OpCode::Var);
 		self.emit_byte(var_id);