To link against system-provided libgit2.

--- a/Cargo.toml
+++ b/Cargo.toml
@@ -39 +39 @@
-git2 = { version="0.14", default-features=false }
+git2 = { version="0.16", default-features=false }
@@ -73,3 +73,4 @@
 [dev-dependencies]
-glassbench = "0.3.3"
+# XXX: depends on old version of broot
+#glassbench = "0.3.3"