Fix Bazel error with nested workspaces. (#45)

See https://github.com/bazelbuild/bazel/issues/3874
diff --git a/WORKSPACE b/WORKSPACE
index a758876..89cbb3c 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 # Used by integration tests
 local_repository(
     name = "test_workspace",
-    path = __workspace_dir__ + "/tests/test_workspace",
+    path = "tests/test_workspace",
 )
 
 # Not actually referenced anywhere, but must be marked as a separate
diff --git a/tests/test_workspace/WORKSPACE b/tests/test_workspace/WORKSPACE
index 27def59..f04d2d0 100644
--- a/tests/test_workspace/WORKSPACE
+++ b/tests/test_workspace/WORKSPACE
@@ -1 +1 @@
-workspace(name = "test_workspace")
\ No newline at end of file
+workspace(name = "test_workspace")