Date literals (#4619)

* Date literals

* update deps

* Add date+duration

src/default_config.nu

@@ -146,6 +146,7 @@ let default_theme = {
     shape_signature: green_bold
     shape_string: green
     shape_string_interpolation: cyan_bold
+    shape_datetime: cyan_bold
     shape_list: cyan_bold
     shape_table: blue_bold
     shape_record: cyan_bold

src/tests/test_engine.rs

@@ -257,3 +257,8 @@ fn test_redirection_stderr() -> TestResult {
     // try a nonsense binary
     run_test(r#"do -i { asdjw4j5cnaabw44rd }; echo done"#, "done")
 }
+
+#[test]
+fn datetime_literal() -> TestResult {
+    run_test(r#"(date now) - 2019-08-23 > 1hr"#, "true")
+}