Drop the rc file flag.

Hopefully no file(s) exists on travis, and with the changes coming in bazel
(bazelbuild/bazel#4502 (comment))
trying to ensure no files will become version dependent.

.travis_build.sh

@@ -19,7 +19,7 @@ set -eu
 # -------------------------------------------------------------------------------------------------
 # Asked to do a bazel build.
 if [[ -n "${BAZEL:-}" ]]; then
-  bazel --bazelrc=/dev/null test --show_progress_rate_limit=30.0 //...
+  bazel test --show_progress_rate_limit=30.0 //...
 fi
 
 # -------------------------------------------------------------------------------------------------