add regression test case for #4

tests/history.rs

@@ -0,0 +1,10 @@
+use tui_textarea::TextArea;
+
+// Regression test for #4
+#[test]
+fn disable_history() {
+    let mut t = TextArea::default();
+    t.set_max_histories(0);
+    assert!(t.insert_str("hello"));
+    assert_eq!(t.lines(), ["hello"]);
+}

tests/mod.rs

@@ -1 +1,2 @@
 mod cursor;
+mod history;