fix: mark apollo-link as peer dependency

Author: Guillaume Chau

package.json

@@ -38,6 +38,7 @@
   "homepage": "https://github.com/Akryum/vue-apollo#readme",
   "peerDependencies": {
     "apollo-client": "^2.0.0",
+    "apollo-link": "^1.0.0",
     "graphql-tag": "^2.10.1"
   },
   "dependencies": {