chore: Updated source to follow clippy suggestions.

src/main.rs

@@ -142,7 +142,7 @@ fn main() {
             let fname = format!("{}", e.path.display());
             let filter_cond = filters
                 .split(',')
-                .filter(|f| f.trim().len() > 0)
+                .filter(|f| !f.trim().is_empty())
                 .any(|f| e.name.contains(&f) || fname.contains(&f));
             let status = if e.looks_done() { "Done" } else { "Pending" };
             let solve_cond = {

tests/integration_tests.rs

@@ -131,7 +131,7 @@ fn all_exercises_require_confirmation() {
             file.read_to_string(&mut s).unwrap();
             s
         };
-        source.matches("// I AM NOT DONE").next().expect(&format!(
+        source.matches("// I AM NOT DONE").next().unwrap_or_else(|| panic!(
             "There should be an `I AM NOT DONE` annotation in {:?}",
             path
         ));