use new varable name for current branch in gitlab ci

Author: rose-a

src/GitVersionCore/BuildServers/GitLabCi.cs

@@ -1,4 +1,4 @@
-namespace GitVersion
+namespace GitVersion
 {
     using System;
     using System.IO;
@@ -37,7 +37,7 @@ public override string[] GenerateSetParameterMessage(string name, string value)
 
         public override string GetCurrentBranch(bool usingDynamicRepos)
         {
-            return Environment.GetEnvironmentVariable("CI_BUILD_REF_NAME");
+            return Environment.GetEnvironmentVariable("CI_COMMIT_REF_NAME");
         }
 
         public override bool PreventFetch()
@@ -57,4 +57,4 @@ void WriteVariablesFile(VersionVariables variables)
             File.WriteAllLines(_file, BuildOutputFormatter.GenerateBuildLogOutput(this, variables));
         }
     }
-}
+}