update mcp kotlin-sdk version to 0.4.0 and update quickstart server kotlin doc (modelcontextprotocol#220)

Author: devcrocod

quickstart/client.mdx

@@ -1015,7 +1015,7 @@ After creating the project, add the following dependencies:
 
 <CodeGroup>
 ```kotlin build.gradle.kts
-val mcpVersion = "0.3.0"
+val mcpVersion = "0.4.0"
 val slf4jVersion = "2.0.9"
 val anthropicVersion = "0.8.0"
 

quickstart/server.mdx

@@ -1090,7 +1090,7 @@ Alternatively, you can create a Kotlin application using the [IntelliJ IDEA proj
 After creating the project, add the following dependencies:
 <CodeGroup>
 ```kotlin build.gradle.kts
-val mcpVersion = "0.3.0"
+val mcpVersion = "0.4.0"
 val slf4jVersion = "2.0.9"
 val ktorVersion = "3.1.1"
 
@@ -1164,7 +1164,7 @@ fun `run mcp server`() {
     runBlocking {
         server.connect(transport)
         val done = Job()
-        server.onCloseCallback = {
+        server.onClose {
             done.complete()
         }
         done.join()