Fix binutils package name.

Test: ./build.py --arch arm64 --host linux
Bug: None
Exempt-From-Owner-Approval: trivially correct
Change-Id: I3339bfa694be929ad44b87d75a4cf3621b58451c
diff --git a/build.py b/build.py
index 6a99aca..840ba56 100755
--- a/build.py
+++ b/build.py
@@ -162,7 +162,7 @@
     else:
         compress_arg = '-j'
 
-    package_path = os.path.join(dist_dir, package_name + 'tar.bz2')
+    package_path = os.path.join(dist_dir, package_name + '.tar.bz2')
     cmd = [
         'tar', compress_arg, '-cf', package_path, '-C', base_dir, package_name,
     ]