Bump version to 1.4.0

Author: jeffhandley

src/Directory.Build.props

@@ -5,7 +5,7 @@
     <PackageProjectUrl>https://csharp.sdk.modelcontextprotocol.io</PackageProjectUrl>
     <RepositoryUrl>https://github.com/modelcontextprotocol/csharp-sdk</RepositoryUrl>
     <RepositoryType>git</RepositoryType>
-    <VersionPrefix>1.3.0</VersionPrefix>
+    <VersionPrefix>1.4.0</VersionPrefix>
     <Authors>ModelContextProtocol</Authors>
     <Copyright>© Model Context Protocol a Series of LF Projects, LLC.</Copyright>
     <PackageTags>ModelContextProtocol;mcp;ai;llm</PackageTags>