[ws server]: use send text instead of send binary

[niklasad1]

Basically because some of common libraries seems to assume that text is the way to go.

[jsdw]

Perhaps unrelated to this PR but; I ran the tests and, while everything passed, I also saw some errors logged to the console that may be related to the change in how messages are being sent?:

test access_control::cors::tests::should_not_allow_partially_matching_origin ... ok
[2021-06-10T10:17:03Z ERROR jsonrpsee_http_server::server] [service_fn], Cannot parse request body="{\"jsonrpc\":\"2.0\",\"method\":\"say_hello\",\"id\"}"
test tests::invalid_json_id_missing_value ... ok
[2021-06-10T10:17:03Z ERROR jsonrpsee_http_server::server] [service_fn], Cannot parse request body="{\"jsonrpc\":\"2.0\",\"method\":\"bar\",\"id\":1,\"is_not_request_object\":1}"
[2021-06-10T10:17:03Z ERROR jsonrpsee_http_server::server] [service_fn], Cannot parse request body="[123]"
test tests::invalid_request_object ... ok
[2021-06-10T10:17:03Z ERROR jsonrpsee_http_server::server] [service_fn], Cannot parse request body="{\"jsonrpc\":\"2.0\",\"method\":1, \"params\": \"bar\"}"
[2021-06-10T10:17:03Z ERROR jsonrpsee_http_server::server] [service_fn], Cannot parse request body="[1, 2, 3]"
test tests::invalid_single_method_call ... ok
test tests::notif_works ... ok
[2021-06-10T10:17:03Z ERROR jsonrpsee_http_server::server] [service_fn], Cannot parse request body="[\n\t\t{\"jsonrpc\": \"2.0\", \"method\": \"sum\", \"params\": [1,2,4], \"id\": \"1\"},\n\t\t{\"jsonrpc\": \"2.0\", \"method\"\n\t  ]"

[niklasad1]

Perhaps unrelated to this PR but; I ran the tests and, while everything passed, I also saw some errors logged to the console that may be related:

It's just because we test with malformed requests to see that they are handled "correctly" and cargo test is multi-threaded by default

[jsdw]

Ah, looking at the test names that makes sense!