llvm-objcopy no longer accepts -strip-all

Apparently --strip-all is the new hotness.

Change-Id: Ifcb8e4c64a6aed01d0a9e309a7244a5bef450e96
diff --git a/src/utils.rs b/src/utils.rs
index bd7c0c1..6b14d2e 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -27,7 +27,7 @@
         .expect("failed to get parent directory of binary to strip")
         .join(new_file_name);
     let strip_result = Command::new(strip_tool_path()?)
-        .arg("-strip-all")
+        .arg("--strip-all")
         .arg(binary)
         .arg(&target_path)
         .status()