Add `apollo-link-http-common` as a dependency (#891)
Add `apollo-link-http-common` as a dependency (#891)

https://github.com/apollographql/apollo-link/pull/530 added
`apollo-link-http-common` as a dev dependency, when it should have
been added as a normal dependency (since it's referenced by the
production version of `apollo-link-error`). This commit switches
it to be a production dependency.

Fixes https://github.com/apollographql/apollo-link/issues/887.
apollographql/apollo-link,apollographql/apollo-link