Fix ability to download windows toolchains on case sensitive unix systems (#797)

diff --git a/python/repositories.bzl b/python/repositories.bzl
index d500ce6..dc2c49e 100644
--- a/python/repositories.bzl
+++ b/python/repositories.bzl
@@ -141,7 +141,7 @@
                     exec_result.stderr,
                 )
                 fail(fail_msg)
-            exec_result = rctx.execute(["touch", "lib/.test"])
+            exec_result = rctx.execute(["touch", "{}/.test".format(lib_dir)])
             if exec_result.return_code == 0:
                 exec_result = rctx.execute(["id", "-u"])
                 if exec_result.return_code != 0: