fix(core): Make @types/fs-extra a dependency

It is required to compile

packages/core/package.json

@@ -41,6 +41,7 @@
     "@nestjs/platform-express": "^6.3.1",
     "@nestjs/testing": "^6.3.1",
     "@nestjs/typeorm": "^6.0.0",
+    "@types/fs-extra": "^7.0.0",
     "@vendure/common": "^0.1.2-beta.5",
     "apollo-server-express": "^2.4.0",
     "bcrypt": "^3.0.6",
@@ -75,7 +76,6 @@
     "@types/csv-parse": "^1.1.11",
     "@types/express": "^4.0.39",
     "@types/faker": "^4.1.4",
-    "@types/fs-extra": "^7.0.0",
     "@types/graphql-iso-date": "^3.3.1",
     "@types/graphql-type-json": "^0.1.3",
     "@types/gulp": "^4.0.5",