Cargo.toml: Add `openssl` explicit dependency
Cargo.toml: Add `openssl` explicit dependency

The nightly Rust channel seems to have lost the ability to transitively
include the full `openssl` crate, when two of its dependencies are
required within a feature.

This commit requires the `openssl` crate itself in the TLS feature to
work around the regression.

stepancheg/solicit,mlalic/solicit,gwicke/solicit,tempbottle/solicit