Many servers will return errors (e.g. 400/403) to requests that do not
set a User-Agent header. This results in issues in both the link_checker
and load_data components. With the link_checker these are false positive
dead links. In load_data, remote data fails to be fetched. To mitigate
this issue, this sets a default User-Agent of
$CARGO_PKG_NAME/$CARGO_PKG_VERSION
Note that the root cause of this regression from zola v0.9.0 is that
reqwest 0.10 changed their default behavior and no longer sets a
User-Agent by default:
https://github.com/seanmonstar/reqwest/pull/751Fixes#950.