Increase minimum `swift-nio-http2` version (#53)

The latest minor release of `swift-nio-http2` (1.35.0) fixes a bug that
would sometimes cause a gRPC server to wedge when TLS setup failed.

This PR increases the minimum version of `swift-nio-http2` required to
make sure this bug isn't present.

Package.swift

@@ -43,7 +43,7 @@ let dependencies: [Package.Dependency] = [
   ),
   .package(
     url: "https://github.com/apple/swift-nio-http2.git",
-    from: "1.34.1"
+    from: "1.35.0"
   ),
   .package(
     url: "https://github.com/apple/swift-nio-transport-services.git",