Bump minimum Bazel version to 0.26.1

Change-Id: I8d6f9eac5af54e5b270e7db4e52d1b4063c1aa56
Signed-off-by: David Ostrovsky <david@ostrovsky.org>
diff --git a/WORKSPACE b/WORKSPACE
index 322e748..d33c116 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -11,7 +11,7 @@
 
 load("@bazel_skylib//lib:versions.bzl", "versions")
 
-versions.check(minimum_bazel_version = "0.19.0")
+versions.check(minimum_bazel_version = "0.26.1")
 
 load("//tools:bazlets.bzl", "load_bazlets")