apply some pedantic lints

src/core.rs

@@ -224,7 +224,7 @@ impl Pacdef {
     fn remove_groups(&self, arg_match: &ArgMatches) -> Result<()> {
         let paths = get_assumed_group_file_names(arg_match)?;
 
-        for file in paths.iter() {
+        for file in &paths {
             ensure!(file.exists(), "did not find the group under {file:?}");
         }
 

src/env.rs

@@ -7,7 +7,7 @@ pub(crate) fn get_editor() -> Result<String> {
 }
 
 fn check_vars_in_order(vars: &[&str]) -> Option<String> {
-    vars.iter().flat_map(|v| var(v).ok()).next()
+    vars.iter().find_map(|v| var(v).ok())
 }
 
 pub(crate) fn get_single_var(variable: &str) -> Option<String> {