use entry to not hash twice thanks clippy

(cherry picked from commit de9a7b9)

Author: Eh2406

src/cargo/ops/cargo_read_manifest.rs

@@ -138,11 +138,13 @@ fn read_nested_packages(path: &Path,
     let pkg = Package::new(manifest, &manifest_path);
 
     let pkg_id = pkg.package_id().clone();
-    if !all_packages.contains_key(&pkg_id) {
-        all_packages.insert(pkg_id, pkg);
-    } else {
-        info!("skipping nested package `{}` found at `{}`",
-              pkg.name(), path.to_string_lossy());
+    use ::std::collections::hash_map::Entry;
+    match all_packages.entry(pkg_id) {
+        Entry::Vacant(v) => { v.insert(pkg); },
+        Entry::Occupied(_) => {
+            info!("skipping nested package `{}` found at `{}`",
+                  pkg.name(), path.to_string_lossy());
+        }
     }
 
     // Registry sources are not allowed to have `path=` dependencies because