Fix 'is_whitespace' error

Author: Xanewok

tests/tests.rs

@@ -1303,9 +1303,8 @@ fn cmd_format_utf16_range() {
         .collect();
     // Actual formatting isn't important - what is, is that the buffer isn't
     // malformed and code stays semantically equivalent.
-    let mut new_text = new_text[0];
-    new_text.retain(|c| !c.is_whitespace());
-    assert_eq!(new_text, "/*😢😢😢😢😢😢😢*/fnmain(){}");
+    let new_text: String = new_text[0].split_whitespace().collect();
+    assert_eq!(&new_text, "/*😢😢😢😢😢😢😢*/fnmain(){}");
 
     rls.shutdown(rls_timeout());
 }