bump version to 2.5.6

appveyor.yml

@@ -1,5 +1,5 @@
 os: Visual Studio 2017
-version: '2.5.5.{build}'
+version: '2.5.6.{build}'
 skip_tags: true
 install:
 - ps: |

src/GitHub.VisualStudio/source.extension.vsixmanifest

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <PackageManifest Version="2.0.0" xmlns="http://schemas.microsoft.com/developer/vsx-schema/2011" xmlns:d="http://schemas.microsoft.com/developer/vsx-schema-design/2011">
   <Metadata>
-    <Identity Id="c3d3dc68-c977-411f-b3e8-03b0dccf7dfc" Version="2.5.5.0" Language="en-US" Publisher="GitHub, Inc" />
+    <Identity Id="c3d3dc68-c977-411f-b3e8-03b0dccf7dfc" Version="2.5.6.0" Language="en-US" Publisher="GitHub, Inc" />
     <DisplayName>GitHub Extension for Visual Studio</DisplayName>
     <Description xml:space="preserve">A Visual Studio Extension that brings the GitHub Flow into Visual Studio.</Description>
     <PackageId>GitHub.VisualStudio</PackageId>

src/common/SolutionInfo.cs

@@ -18,6 +18,6 @@
 namespace System
 {
     internal static class AssemblyVersionInformation {
-        internal const string Version = "2.5.5.0";
+        internal const string Version = "2.5.6.0";
     }
 }