update with command variables

.circleci/config.yml

@@ -1,5 +1,17 @@
 version: 2.1 
 
+commands:
+    restore_cache_cmd:
+      steps:
+        - restore_cache:
+            key: yarn-v1-packages-{{ checksum "yarn.lock" }}
+    save_cache_cmd:
+      steps:
+        - save_cache:
+            paths:
+              - ./node_modules
+            key: yarn-v1-packages-{{ checksum "yarn.lock" }}
+
 jobs:
   build:
     docker:
@@ -7,12 +19,8 @@ jobs:
 
     steps:
       - checkout
-      - restore_cache:
-          key: yarn-v1-packages-{{ checksum "yarn.lock" }}
+      - restore_cache_cmd
       - run: 
           command: "yarn global add node-gyp && yarn install"
           name: "installation"
-      - save_cache:
-          key: yarn-v1-packages-{{ checksum "yarn.lock" }}
-          paths:
-            - ./node_modules
+      - save_cache_cmd