Bump Java language level to Java 11

Follow up to JGit and Gerrit project, that switched to Java
language level 11.

One side effect of this change is that tools/eclipse/project.sh script
is using bazlets and JavaSE-1.8 is still generated there. In follow up
change Bazlets version will be updated to generate Java 11 compatible
eclipse project.

Change-Id: I488bc6e148e41dfdaef9dcf8b1031df1d22a582d

tools/BUILD

diff --git a/tools/BUILD b/tools/BUILD
index 5cfe48c..ec76f1b 100644
--- a/tools/BUILD
+++ b/tools/BUILD
@@ -1,14 +1,13 @@
 load(
     "@bazel_tools//tools/jdk:default_java_toolchain.bzl",
-    "JDK9_JVM_OPTS",
     "default_java_toolchain",
 )
 load("@rules_java//java:defs.bzl", "java_package_configuration")
 
 default_java_toolchain(
-    name = "error_prone_warnings_toolchain",
-    bootclasspath = ["@bazel_tools//tools/jdk:platformclasspath.jar"],
-    jvm_opts = JDK9_JVM_OPTS,
+    name = "error_prone_warnings_toolchain_java11",
+    source_version = "11",
+    target_version = "11",
     package_configuration = [
         ":error_prone",
     ],