use xliiv:upgrade-x11 branch of rust-clipboard

The rust-clipboard project's maintenance status is [unclear][1].

It pulls in an old version of [ruxt-xcb][2]. This old version has a
[security issue][3]. It also has a complex build that caused failures I
could not debug when building dmenu-rs with nix.

There is an [open PR][4] to rust-clipboard that updates the X11 and XCB
dependencies with a minimal changeset, resolving this issue.

This commit updates dmenu-rs's rust-clipboard dependency to point to the
fix in the open PR, located on the upgrade-x11 branch of xliiv's fork.

You can find similar discussion in an unrelated project [here][5].

[1]: aweinstock314/rust-clipboard#91
[2]: https://github.com/rust-x-bindings/rust-xcb/tree/v0.8.2
[3]: aweinstock314/rust-clipboard#90
[4]: aweinstock314/rust-clipboard#89
[5]: iceiix/stevenarella#701

src/build/CargoSource.toml

@@ -15,7 +15,7 @@ path = "../dmenu/main.rs"
 
 [dependencies]
 clap = { version = "2.33.1", features = ["yaml"]}
-clipboard = "0.5"
+clipboard = { git = "https://github.com/xliiv/rust-clipboard", branch = "upgrade-x11" }
 itertools = "0.9"
 lazy_static = "1.4.0"
 libc = "0.2.69"
@@ -37,4 +37,4 @@ termcolor = "1.1"
 
 [features]
 Xinerama = []
-default = ["Xinerama"]
+default = ["Xinerama"]