Go: bump to 1.15.5

The new Go release fixes the following security issues:

CVE-2020-28362, CVE-2020-28367, CVE-2020-28366

See https://groups.google.com/g/golang-announce/c/NpBGTTmKzpM for more
detail.

The next step will be to re-build all our production Go binaries.

Change-Id: I97e4678a2e06a9559e66c0c0db008f0b6dfd81a2
diff --git a/WORKSPACE b/WORKSPACE
index ed9de43..9dd649c 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -40,10 +40,10 @@
 # Download Go/Gazelle rules
 http_archive(
     name = "io_bazel_rules_go",
-    sha256 = "d1ffd055969c8f8d431e2d439813e42326961d0942bdf734d2c95dc30c369566",
+    sha256 = "207fad3e6689135c5d8713e5a17ba9d1290238f47b9ba545b63d9303406209c6",
     urls = [
-        "https://mirror.bazel.build/github.com/bazelbuild/rules_go/releases/download/v0.24.5/rules_go-v0.24.5.tar.gz",
-        "https://github.com/bazelbuild/rules_go/releases/download/v0.24.5/rules_go-v0.24.5.tar.gz",
+        "https://mirror.bazel.build/github.com/bazelbuild/rules_go/releases/download/v0.24.7/rules_go-v0.24.7.tar.gz",
+        "https://github.com/bazelbuild/rules_go/releases/download/v0.24.7/rules_go-v0.24.7.tar.gz",
     ],
 )
 http_archive(