option link not work when option websocketsOnly=true

[gaoyuan123]

Describe the bug
option link not work when option websocketsOnly=true,because vue-cli-plugin-apollo/graphql-client/src/index.js line 127 rewrite the link option.

if (disableHttp) {
        link = wsLink
      } else {
        link = split(
          // split based on operation type
          ({ query }) => {
            const { kind, operation } = getMainDefinition(query)
            return kind === 'OperationDefinition' &&
              operation === 'subscription'
          },
          wsLink,
          link
        )
      }

Versions
vue-cli-plugin-apollo:0.21.3