case-sensitive "keep-alive" causes errors

[CharlesOkwuagwu]

These clauses are case-sensitive. That can lead to problems like the one I just caught.

[14:44:05.119] Elli request (pid #PID<0.407.0>) unexpectedly crashed:

{{:case_clause, "keep-alive"},
 [
   {:elli_http, :close_or_keepalive, 2,
    [file: ~c"c:/Projects/elli-4.0.0/src/elli_http.erl", line: 687]},
   {:elli_http, :handle_response, 3,
    [file: ~c"c:/Projects/elli-4.0.0/src/elli_http.erl", line: 148]},
   {:elli_http, :keepalive_loop, 5,
    [file: ~c"c:/Projects/elli-4.0.0/src/elli_http.erl", line: 83]},
   {:proc_lib, :init_p_do_apply, 3, [file: ~c"proc_lib.erl", line: 241]}
 ]}

[tsloughter]

Thanks, yea, it should probably downcase all headers when reading the request in the first place.