Fixed duplicate-ack for serial execution services

- Moved to 0.1.5.1

src/Holon/Holon.csproj

@@ -2,19 +2,19 @@
 
   <PropertyGroup>
     <TargetFramework>netstandard1.6</TargetFramework>
-    <Version>0.1.5</Version>
+    <Version>0.1.5.1</Version>
     <Authors>Alan Doherty</Authors>
     <Company>Alan Doherty</Company>
     <Description>A minimal service and event bus with additional support for RPC</Description>
     <Copyright>BattleCrate Ltd 2018</Copyright>
     <PackageProjectUrl>https://github.com/alandoherty/holon-net</PackageProjectUrl>
     <RepositoryUrl>https://github.com/alandoherty/holon-net</RepositoryUrl>
     <RepositoryType>git</RepositoryType>
-    <AssemblyVersion>0.1.5.0</AssemblyVersion>
+    <AssemblyVersion>0.1.5.1</AssemblyVersion>
     <PackageLicenseUrl>https://github.com/alandoherty/holon-net/blob/master/LICENSE</PackageLicenseUrl>
     <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
     <PackageIconUrl>https://s3-eu-west-1.amazonaws.com/assets.alandoherty.co.uk/github/holon-net-nuget.png</PackageIconUrl>
-    <FileVersion>0.1.5.0</FileVersion>
+    <FileVersion>0.1.5.1</FileVersion>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">

src/Holon/Services/Service.cs

@@ -317,6 +317,8 @@ async void IObserver<InboundMessage>.OnNext(InboundMessage message) {
                     // decrement pending metric and increment completed
                     Interlocked.Decrement(ref _requestsPending);
                     Interlocked.Increment(ref _requestsCompleted);
+
+                    return;
                 } else {
                     ServiceHandle(envelope);
                 }