Bump Bazel version to 4.0.0

Change-Id: I06072449cf14e80f7c5e585ee97a02f86cb75bd8
diff --git a/.bazelversion b/.bazelversion
index 7c69a55d..fcdb2e1 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-3.7.0
+4.0.0