refactor/polish ~ fix cargo clippy complaints (unneeded String::from)

src/mktemp/mktemp.rs

@@ -186,7 +186,7 @@ pub fn dry_exec(mut tmpdir: PathBuf, prefix: &str, rand: usize, suffix: &str) ->
             }
         }
     }
-    tmpdir.push(String::from(buf));
+    tmpdir.push(buf);
     println!("{}", tmpdir.display());
     0
 }

src/ptx/ptx.rs

@@ -249,7 +249,7 @@ fn create_word_set(
                 }
                 word_set.insert(WordRef {
                     word: word,
-                    filename: String::from(file.clone()),
+                    filename: file.clone(),
                     global_line_nr: offs + count,
                     local_line_nr: count,
                     position: beg,