Make bindgen dep match libnfs-sys

This is to avoid a clash over clang-sys. Workaround for cargo bug rust-lang/cargo#5237.

Author: jsgf

Cargo.toml

@@ -13,7 +13,7 @@ keywords = ["ffi", "libffi", "closure", "c"]
 [dependencies]
 
 [build-dependencies]
-bindgen = "0.31.3"
+bindgen = "0.40.0" # match libnfs-sys 0.2.0
 make-cmd = "0.1"
 pkg-config = "0.3.13"