updating git logic to work on detached head

tests/QA/module.tests.ps1

@@ -14,9 +14,12 @@ $SourcePath = (Get-ChildItem $ProjectPath\*\*.psd1 | Where-Object {
 
     Describe 'Changelog Management' -Tag 'Changelog' {
         It 'Changelog has been updated' -skip:(![bool](Get-Command git -EA SilentlyContinue)) {
-            $filesChanged = &git diff master.. --name-only # Get the list of changed files compared with master
-            $currentBranch = &git rev-parse --abbrev-ref HEAD
-            if($currentBranch -ne 'master') {
+            # Get the list of changed files compared with master
+            $HeadCommit = &git rev-parse HEAD
+            $MasterCommit = &git rev-parse origin/master
+            $filesChanged = &git diff $MasterCommit...$HeadCommit --name-only
+
+            if($HeadCommit -ne $MasterCommit) { # if we're not testing same commit (i.e. master..master)
                 $filesChanged.Where{ (Split-Path $_ -Leaf) -match '^changelog' } | Should -Not -BeNullOrEmpty
             }
         }