Update Cargo.toml post-release of v0.7.0-rc.0

We update the `Cargo.toml` after pushing out the release.

Author: tnull

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ldk-node"
-version = "0.7.0+git"
+version = "0.7.0-rc.0"
 authors = ["Elias Rohrer <dev@tnull.de>"]
 homepage = "https://lightningdevkit.org/"
 license = "MIT OR Apache-2.0"