cargo-new should not add ignore rule on Cargo.lock inside subdirs

Have traced down the issue. It feel like the original intent is to
ignore `Cargo.lock` and `target` at project root but not subdirectories.

1. The original implementation did ignore root `/Cargo.lock`.
   #321
2. Someday one wanted to support both gitignore and hgingore's syntax
   and removed the leading slash.
   #1247
3. Later, one found that we should not ignore `target` other than
   under root directory and added `/target` back.
   #4099
4. It turns out that the syntax is not compatible between gitignore
   and hgignore. Therefore, one started to use hgignore special syntax
   to handle `Cargo.lock`.
   #4342

This commit rollbacks to what original implementation tries to do.

Author: weihanglo

src/cargo/ops/cargo_new.rs

@@ -716,7 +716,7 @@ fn mk(config: &Config, opts: &MkOptions<'_>) -> CargoResult<()> {
     let mut ignore = IgnoreList::new();
     ignore.push("/target", "^target/", "target");
     if !opts.bin {
-        ignore.push("Cargo.lock", "glob:Cargo.lock", "Cargo.lock,*/Cargo.lock");
+        ignore.push("/Cargo.lock", "^Cargo.lock$", "Cargo.lock");
     }
 
     let vcs = opts.version_control.unwrap_or_else(|| {