Try using similar rather than difflib

Gives much better diffs when lines are inserted

Fixes #755

Cargo.toml

@@ -88,6 +88,7 @@ trycmd = "0.14.21"
 anyhow = "1.0.79"
 concolor-control = { version = "0.0.7", features = ["auto"] }
 git-conventional = "0.12.4"
+similar = "2.4"
 
 [dev-dependencies]
 assert_fs = "1.1"

src/ops/replace.rs

@@ -1,6 +1,8 @@
 use std::collections::BTreeMap;
 use std::path::Path;
 
+use similar::TextDiff;
+
 use crate::config::Replace;
 use crate::error::CargoResult;
 
@@ -118,25 +120,15 @@ pub fn do_file_replacements(
 
         if data != replaced {
             if dry_run {
-                let display_path = path.display().to_string();
-                let data_lines: Vec<_> = data.lines().map(|s| format!("{}\n", s)).collect();
-                let replaced_lines: Vec<_> = replaced.lines().map(|s| format!("{}\n", s)).collect();
-                let diff = difflib::unified_diff(
-                    &data_lines,
-                    &replaced_lines,
-                    display_path.as_str(),
-                    display_path.as_str(),
-                    "original",
-                    "replaced",
-                    0,
-                );
                 if noisy {
+                    let diff = TextDiff::from_lines(&data, &replaced);
+                    let display_path = path.display().to_string();
                     let _ = crate::ops::shell::status(
                         "Replacing",
                         format!(
                             "in {}\n{}",
                             path.display(),
-                            itertools::join(diff.into_iter(), "")
+                            diff.unified_diff().header(&display_path, &display_path)
                         ),
                     );
                 } else {