Changing the directory to '.' doesn't modify the prompt anymore (#2457)

Doing 'cd .' or an equal command used to modify the prompt: It appended an './' and was even
repeatable, leading to strange prompts (believe me, I tested it for too long).

This fixes #2432

crates/nu-cli/src/path.rs

@@ -6,7 +6,14 @@ where
     P: AsRef<Path>,
     Q: AsRef<Path>,
 {
-    let path = relative_to.as_ref().join(path);
+    let path = if path.as_ref() == Path::new(".") {
+        // Joining a Path with '.' appends a '.' at the end, making the prompt
+        // more ugly - so we don't do anything, which should result in an equal
+        // path on all supported systems.
+        relative_to.as_ref().to_owned()
+    } else {
+        relative_to.as_ref().join(path)
+    };
 
     let (relative_to, path) = {
         let components: Vec<_> = path.components().collect();