Bump bazel version to 2.0.0

Also bump bazlets to the latest master revision.

Change-Id: Ia984bc9250b8c2a8dc03458e2c910fadb1ef6149

.bazelversion

diff --git a/.bazelversion b/.bazelversion
index 26aaba0..227cea2 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-1.2.0
+2.0.0