Fix accidental printing of files named 'cache'

This also adds two regression tests, so this will hopefully not pop up
again.

closes #557

tests/integration_tests.rs

@@ -448,3 +448,18 @@ fn utf16() {
         .success()
         .stdout(std::str::from_utf8(b"\xEF\xBB\xBFhello world\n").unwrap());
 }
+
+#[test]
+fn can_print_file_named_cache() {
+    bat()
+        .arg("cache")
+        .assert()
+        .success()
+        .stdout("test\n")
+        .stderr("");
+}
+
+#[test]
+fn does_not_print_unwanted_file_named_cache() {
+    bat_with_config().arg("cach").assert().failure();
+}