don't put placeholder in

Author: Oren Novotny

src/GitVersionCore.Tests/BuildServers/VsoAgentTests.cs

@@ -9,7 +9,9 @@ public void Develop_branch()
     {
         var versionBuilder = new VsoAgent();
         var vsVersion = versionBuilder.GenerateSetVersionMessage("0.0.0-Unstable4");
-        Assert.AreEqual("##vso[task.setvariable variable=GitBuildNumber;]0.0.0-Unstable4", vsVersion);
+        //  Assert.AreEqual("##vso[task.setvariable variable=GitBuildNumber;]0.0.0-Unstable4", vsVersion);
+
+        Assert.Null(vsVersion);
     }
 
     [Test]

src/GitVersionCore/BuildServers/VsoAgent.cs

@@ -20,8 +20,7 @@ public override string[] GenerateSetParameterMessage(string name, string value)
         public override string GenerateSetVersionMessage(string versionToUseForBuildNumber)
         {
             // Note: the VSO agent does not yet support updating the build display number from a variable
-            // this is here for later when they do but might need adjusting
-            return string.Format("##vso[task.setvariable variable=GitBuildNumber;]{0}", versionToUseForBuildNumber);
+            return null;
         }
     }
 }