Bump Bazel version to 3.7.0

This release has these changes [1]. Skip the 3.6.0 release [2], as both
happened quickly compared to the pace of this maintenance. Notes [1,2]
are linked from [3], alongside changes that were cherry-picks.

[1] https://blog.bazel.build/2020/10/20/bazel-3-7.html
[2] https://blog.bazel.build/2020/10/06/bazel-3-6.html
[3] https://github.com/bazelbuild/bazel/releases

Change-Id: I4694caaec579e1ece4537f9a46a585226489354a
diff --git a/.bazelversion b/.bazelversion
index d5c0c99..7c69a55 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-3.5.1
+3.7.0