Update libc to 0.2.171 to meet cygwin's requirement
diff --git a/Cargo.lock b/Cargo.lock
index 38b5fe1..e4a21b7 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -93,9 +93,9 @@
 
 [[package]]
 name = "libc"
-version = "0.2.159"
+version = "0.2.171"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "561d97a539a36e26a9a5fad1ea11a3039a67714694aaa379433e580854bc3dc5"
+checksum = "c19937216e9d3aa9956d9bb8dfc0b0c8beb6058fc4f7a4dc4d850edf86a237d6"
 
 [[package]]
 name = "libloading"