Update bindgen to 0.51

pcpthm · web-flow · commit e6c8b512ef66 · 2019-10-20T03:23:46.000+09:00
A bug rust-lang/rust-bindgen#1627 causes compilation failure in nightly compiler.
diff --git a/Cargo.toml b/Cargo.toml
@@ -14,5 +14,5 @@ categories = ["multimedia::audio"]
 all_asserts = "0.1.4"
 
 [build-dependencies]
-bindgen = "0.49"
+bindgen = "0.51"
 pathdiff = "0.1"
