chore: set desired npm version to 7 (#533)

package-lock.json

@@ -56,7 +56,8 @@
         "typescript": "^4.2.4"
       },
       "engines": {
-        "node": "14.x"
+        "node": "14.x",
+        "npm": "7.x"
       }
     },
     "node_modules/@ampproject/toolbox-core": {

package.json

@@ -72,9 +72,11 @@
     "typescript": "^4.2.4"
   },
   "engines": {
-    "node": "14.x"
+    "node": "14.x",
+    "npm": "7.x"
   },
   "volta": {
-    "node": "14.15.5"
+    "node": "14.15.5",
+    "npm": "7.19.0"
   }
 }