Bump Bazel version to 4.0.0

Change-Id: Icd78b4ef1f8f0563d26aa14f6d0c77f3e49a9667
diff --git a/.bazelversion b/.bazelversion
index 7c69a55..fcdb2e1 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-3.7.0
+4.0.0