Reduce max HTTP dependency version to v0.6.14
HTTP v0.6.15 changed the API by removing the compat module, which is refererred in default keyword arguments in WebSockets.ServeWS. Previous upper limit was v0.6.99.
HTTP v0.6.15 changed the API by removing the compat module, which is refererred in default keyword arguments in WebSockets.ServeWS. Previous upper limit was v0.6.99.