Require minimum Bazel version 0.19.0

Change-Id: Idd85e245b46969c87417714d0f0c30336e1d67bd
diff --git a/tools/BUILD b/tools/BUILD
index a2561ad..7760b20 100644
--- a/tools/BUILD
+++ b/tools/BUILD
@@ -13,7 +13,7 @@
 
 default_java_toolchain(
     name = "error_prone_warnings_toolchain",
-    bootclasspath = ["@bazel_tools//tools/jdk:platformclasspath9.jar"],
+    bootclasspath = ["@bazel_tools//tools/jdk:platformclasspath.jar"],
     jvm_opts = JDK9_JVM_OPTS,
     package_configuration = [
         ":error_prone",