hg-cpython: upgrade dependencies

`hg-cpython` has no BC breaking dependencies, we can group them all
in this changeset.

rust/hg-cpython/Cargo.toml

@@ -9,11 +9,11 b" name='rusthg'"
 crate-type = ["cdylib"]
 
 [dependencies]
-cpython = { version = "0.7.0", features = ["extension-module"] }
-crossbeam-channel = "0.5.2"
+cpython = { version = "0.7.1", features = ["extension-module"] }
+crossbeam-channel = "0.5.6"
 hg-core = { path = "../hg-core"}
-libc = "0.2.119"
-log = "0.4.14"
-env_logger = "0.9.0"
+libc = "0.2.137"
+log = "0.4.17"
+env_logger = "0.9.3"
 stable_deref_trait = "1.2.0"
 vcsgraph = "0.2.0"