bazel: assert if '-Swift.h' files are not exactly 1 (#374)
bazel: assert if '-Swift.h' files are not exactly 1 (#374)

Addressing https://github.com/lyft/envoy-mobile/pull/372#discussion_r316845384

Signed-off-by: Michael Rebello <b1c1d8736f20db3fb6c1c66bb1455ed43909f0d8@michaelrebello.com>
envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile