Fix Go compilation (#284)

Before this commit, tests fail with:

(18:39:29) ERROR: /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/ec321eb2cc2d0f8f91b676b6d4c66c29/external/io_bazel_rules_go/BUILD.bazel:71:16: in (an implicit dependency) attribute of go_context_data rule @@io_bazel_rules_go//:go_context_data: in $whitelist_function_transition attribute of go_context_data rule @@io_bazel_rules_go//:go_context_data: package group '@@bazel_tools//tools/whitelists/function_transition_whitelist:function_transition_whitelist' is misplaced here (they are only allowed in the visibility attribute)

(https://buildkite.com/bazel/starlark/builds/2181#01910a16-5592-4949-8b24-6f6dbf212e6f)

WORKSPACE

@@ -86,10 +86,10 @@ maven_install(
 
 http_archive(
     name = "io_bazel_rules_go",
-    sha256 = "56d8c5a5c91e1af73eca71a6fab2ced959b67c86d12ba37feedb0a2dfea441a6",
+    sha256 = "d93ef02f1e72c82d8bb3d5169519b36167b33cf68c252525e3b9d3d5dd143de7",
     urls = [
-        "https://mirror.bazel.build/github.com/bazelbuild/rules_go/releases/download/v0.37.0/rules_go-v0.37.0.zip",
-        "https://github.com/bazelbuild/rules_go/releases/download/v0.37.0/rules_go-v0.37.0.zip",
+        "https://mirror.bazel.build/github.com/bazelbuild/rules_go/releases/download/v0.49.0/rules_go-v0.49.0.zip",
+        "https://github.com/bazelbuild/rules_go/releases/download/v0.49.0/rules_go-v0.49.0.zip",
     ],
 )