Add a backward compatible way of getting random bytes

[jonalmeida]

Should allow you to keep using an older version of OTP with rand_bytes/1 otherwise uses strong_rand_bytes/1

[jonalmeida]

CI fails because of Reason: {badmatch,{error,{"no such file or directory","cowlib.app"}}}. I'm not sure how to fix that.

[sb8244]

crypto.rand_bytes is deprecated in erlang/OTP 20. I believe that this PR fixes the error by using strong_rand_bytes. @jonalmeida have you been able to publish a module up that would fix this, or waiting for merge here?

[jonalmeida]

@sb8244 Waiting for merge and/or someone to fix the CI build since it's not related to this.

[sb8244]

Thanks for the update @jonalmeida. I'm still seeing some issues with the code that I'm trying to get working, although it could be related to that library and not this one. I actually see that websocket_client master has the strong_rand_bytes which is what I needed (not backwards compat)