Dependency version requirements are too restrictive

[moogle19]

The version in the mix.exs are quite restrictive:

{:websock, "~> 0.4.3"},
{:plug, "~> 1.14.0"},
{:bandit, "~> 0.5.9", optional: true},

Currently bandit 0.6.0 won't work without specifying override: true.

Can we switch it to go up to the next major version (e.g. {:bandit, "~> 0.5"}) for all three?

[mtrudel]

Done & published as 0.4.5