fix(composable): fix infinite loading in ssr

[negezor]

There is no $isServer property in the Composition API for Vue 2. This causes an infinite load on the server.

https://github.com/vuejs/composition-api/blob/master/CHANGELOG.md#100-beta22-2020-12-19

// vm.$isServer undefined
console.log('vm.$isServer', vm.$isServer);
// vm.proxy.$isServer true
console.log('vm.proxy.$isServer', vm.proxy.$isServer);

Issue with reproducible error #1222, repository https://github.com/negezor/nuxt-apollo-3-slow-ssr

[negezor]

@Akryum could you check that?

[Akryum]

Thanks for the PR! I fixed the issue differently