cargo update -p futures --aggressive

    Updating futures v0.3.4 -> v0.3.5
    Updating futures-channel v0.3.4 -> v0.3.5
    Updating futures-core v0.3.4 -> v0.3.5
    Updating futures-executor v0.3.4 -> v0.3.5
    Updating futures-io v0.3.4 -> v0.3.5
    Updating futures-macro v0.3.4 -> v0.3.5
    Updating futures-sink v0.3.4 -> v0.3.5
    Updating futures-task v0.3.4 -> v0.3.5
    Updating futures-util v0.3.4 -> v0.3.5
      Adding once_cell v1.4.0
    Updating proc-macro2 v1.0.12 -> v1.0.13
    Updating quote v1.0.4 -> v1.0.6
    Updating syn v1.0.18 -> v1.0.22

Author: JohnTitor