Update bazel to 5.1.0

This was pinned to an old version of bazel, which also doesn't support
building on M1 Macs

Change-Id: I0c5b76def84d03e9aaa7763e18caabd4fd1a584f

.bazelversion

diff --git a/.bazelversion b/.bazelversion
index 40c341b..831446c 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-3.6.0
+5.1.0