cargo update silently fails to update dependencies

[debris]

cargo 0.20.0 (a60d185 2017-07-13)

# Cargo.toml

[dependencies]
bigint = "4.0"
crunchy = "0.1.3"

# Cargo.lock

[root]
name = "bigint_test"
version = "0.1.0"
dependencies = [
 "bigint 4.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
 "crunchy 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
]

# ...

bigint 4.1.2 depends on crunchy 0.1.5
bigint 4.1.1 depends on crunchy 0.1.3

---

running

cargo update -p bigint

results in no updates at all. Only update message is displayed.

    Updating registry `https://github.com/rust-lang/crates.io-index`

---

running

cargo update

results in all creates being updated

    Updating registry `https://github.com/rust-lang/crates.io-index`
    Updating bigint v4.1.1 -> v4.1.2
    Updating crunchy v0.1.3 -> v0.1.6

---

How it could be improved?

Running cargo update -p should result in warning when new version of crate is available, but the update is not possible

The bug can be reproduced using this repo

[alexcrichton]

Ah ok I think this is just an instance of #4066 and #4127, so I'm going to close this in favor of those two issues.