update h2o.cr (#5890)

frameworks/Crystal/h2o.cr/benchmark_config.json

@@ -4,7 +4,7 @@
     {
       "default": {
         "json_url": "/json",
-        "plaintext_url": "/hello",
+        "plaintext_url": "/plaintext",
         "port": 7890,
         "approach": "Realistic",
         "classification": "Micro",

frameworks/Crystal/h2o.cr/h2o_evloop_hello.cr

@@ -95,7 +95,7 @@ class H2oHello < H2o
     @config.server_name = h2o_iovec_init("h2o")
 
     hostconf = h2o_config_register_host(pointerof(@config), h2o_iovec_init("default"), 65535)
-    register_handler(hostconf, "/hello", hello)
+    register_handler(hostconf, "/plaintext", hello)
     register_handler(hostconf, "/json", json)
 
     h2o_context_init(pointerof(@ctx), @loop, pointerof(@config))