remove redundant clones in exercise examples (#1016)

Author: coriolinus

exercises/book-store/example.rs

@@ -154,7 +154,7 @@ impl Iterator for DecomposeGroups {
                     let mut book_iter = backing_bt.iter();
                     *book_iter.next().unwrap()
                 };
-                hypothetical = groups.clone();
+                hypothetical = groups;
                 hypothetical[0].0.borrow_mut().remove(&book);
                 hypothetical.push(Group::new_containing(book));
                 hypothetical.sort();

exercises/grep/example.rs

@@ -67,9 +67,9 @@ pub fn grep(pattern: &str, flags: &Flags, files: &[&str]) -> Result<Vec<String>,
                     let mut inner_pattern = String::from(pattern);
 
                     if flags.use_caseinsensitive_comparison {
-                        inner_line = inner_line.to_lowercase().to_string();
+                        inner_line = inner_line.to_lowercase();
 
-                        inner_pattern = inner_pattern.to_lowercase().to_string();
+                        inner_pattern = inner_pattern.to_lowercase();
                     }
 
                     if flags.use_inverted_comparison {