Add `inputs.nixpkgs.follows` to `rust-overlay` in `flake.nix` (#1729)

* add `inputs.nixpkgs.follows` to `rust-overlay`

* Update flake.lock

flake.lock

@@ -70,22 +70,6 @@
         "type": "github"
       }
     },
-    "nixpkgs_2": {
-      "locked": {
-        "lastModified": 1637453606,
-        "narHash": "sha256-Gy6cwUswft9xqsjWxFYEnx/63/qzaFUwatcbV5GF/GQ=",
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "8afc4e543663ca0a6a4f496262cd05233737e732",
-        "type": "github"
-      },
-      "original": {
-        "owner": "NixOS",
-        "ref": "nixpkgs-unstable",
-        "repo": "nixpkgs",
-        "type": "github"
-      }
-    },
     "root": {
       "inputs": {
         "nixCargoIntegration": "nixCargoIntegration",
@@ -96,7 +80,9 @@
     "rust-overlay": {
       "inputs": {
         "flake-utils": "flake-utils",
-        "nixpkgs": "nixpkgs_2"
+        "nixpkgs": [
+          "nixpkgs"
+        ]
       },
       "locked": {
         "lastModified": 1642128126,

flake.nix

@@ -3,7 +3,10 @@
 
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
-    rust-overlay.url = "github:oxalica/rust-overlay";
+    rust-overlay = {
+      url = "github:oxalica/rust-overlay";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
     nixCargoIntegration = {
       url = "github:yusdacra/nix-cargo-integration";
       inputs.nixpkgs.follows = "nixpkgs";