Switch required bazel version to 0.29.1

Based on the corresponding core change series started with Ib48fdbb6.

Change-Id: I9da552aa411f15b7f3b8a4e541c1fb07d4f70cf2
diff --git a/.bazelversion b/.bazelversion
index 8862dba..25939d3 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-1.0.0rc2
+0.29.1