Make the build work again with Bazel version 0.23.0+

Author: meisterT

WORKSPACE

@@ -1,12 +1,14 @@
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive", "http_jar")
+
 http_jar(
     name = "antlr4",
     sha256 = "f41dce7441d523baf9769cb7756a00f27a4b67e55aacab44525541f62d7f6688",
     url = "https://www.antlr.org/download/antlr-4.7.1-complete.jar",
 )
 
-new_http_archive(
+http_archive(
     name = "antlr4_cpp_runtime",
-    build_file = "BUILD.antlr4_cpp_runtime",
+    build_file = "@//:BUILD.antlr4_cpp_runtime",
     sha256 = "4d0714f441333a63e50031c9e8e4890c78f3d21e053d46416949803e122a6574",
     strip_prefix = "antlr4-4.7.1/runtime/Cpp",
     url = "https://github.com/antlr/antlr4/archive/4.7.1.tar.gz",
@@ -26,9 +28,9 @@ http_archive(
     url = "https://github.com/abseil/abseil-cpp/archive/e5be80532b5d998813f9db952d2cc5401b1532df.tar.gz",
 )
 
-new_http_archive(
+http_archive(
     name = "cpp_btree",
-    build_file = "BUILD.cpp_btree",
+    build_file = "@//:BUILD.cpp_btree",
     sha256 = "e86d047ef509d70f706d526301dc64b6935826d38649f834de49cd11a3018d01",
     strip_prefix = "cpp-btree-92ec61e4b8bf182c5c49ebf6540dac62d569d090",
     url = "https://github.com/algorithm-ninja/cpp-btree/archive/92ec61e4b8bf182c5c49ebf6540dac62d569d090.tar.gz",