Bazel: Bump minimum supported version to 0.26.1

Also harmonize the version used for Bazelisk to the same version.

Change-Id: I084a4b260e2731b28aef3da37aa815bd06bf6a8d
diff --git a/.bazelversion b/.bazelversion
index b2525e3..260bb30 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1,2 @@
-0.27.0rc3
\ No newline at end of file
+0.26.1
+
diff --git a/WORKSPACE b/WORKSPACE
index af54b0f..861398e 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -65,7 +65,7 @@
 
 load("@bazel_skylib//lib:versions.bzl", "versions")
 
-versions.check(minimum_bazel_version = "0.25.0")
+versions.check(minimum_bazel_version = "0.26.1")
 
 load("@io_bazel_rules_closure//closure:defs.bzl", "closure_repositories")