problem: no response from proxy if upstream returned error

fix: #35

testing/dshackle/README.adoc

@@ -0,0 +1,7 @@
+= Testing Server
+
+.Run from project root directory:
+[source,bash]
+----
+./gradlew run --args="--configPath=./testing/dshackle/dshackle.yaml"
+----

testing/dshackle/dshackle.yaml

@@ -0,0 +1,28 @@
+version: v1
+port: 12448
+
+tls:
+  enabled: false
+
+cluster:
+  upstreams:
+    - id: test-1
+      chain: ethereum
+      options:
+        disable-validation: true
+      connection:
+        ethereum:
+          rpc:
+            url: "http://localhost:18545"
+
+cache:
+  redis:
+    enabled: false
+
+proxy:
+  port: 18080
+  tls:
+    enabled: false
+  routes:
+    - id: eth
+      blockchain: ethereum