unstable-book-gen: fix clippy::single_char_pattern and clippy::iter_skip_next

Author: matthiaskrgr

src/tools/tidy/src/error_codes_check.rs

@@ -56,7 +56,7 @@ fn check_if_error_code_is_test_in_explanation(f: &str, err_code: &str) -> bool {
         if s.starts_with("```") {
             if s.contains("compile_fail") && s.contains(err_code) {
                 return true;
-            } else if s.contains("(") {
+            } else if s.contains('(') {
                 // It's very likely that we can't actually make it fail compilation...
                 return true;
             }

src/tools/unstable-book-gen/src/main.rs

@@ -94,9 +94,9 @@ fn copy_recursive(from: &Path, to: &Path) {
 }
 
 fn main() {
-    let library_path_str = env::args_os().skip(1).next().expect("library path required");
-    let src_path_str = env::args_os().skip(2).next().expect("source path required");
-    let dest_path_str = env::args_os().skip(3).next().expect("destination path required");
+    let library_path_str = env::args_os().nth(1).expect("library path required");
+    let src_path_str = env::args_os().nth(2).expect("source path required");
+    let dest_path_str = env::args_os().nth(3).expect("destination path required");
     let library_path = Path::new(&library_path_str);
     let src_path = Path::new(&src_path_str);
     let dest_path = Path::new(&dest_path_str);