Add 3.0.x branch handling to appveyor-install.ps1

BuildTools/appveyor-install.ps1

@@ -3,6 +3,8 @@ $ErrorActionPreference = "Stop"
 $baseCommit = "d779383cb85003d6dabeb976f0845631e07bf463";
 $baseCommitRev = 1;
 
+$masterBranches = @("master", "3.0.x");
+
 $globalAssemblyInfoTemplateFile = "ILSpy/Properties/AssemblyInfo.template.cs";
 
 $versionParts = @{};
@@ -18,10 +20,10 @@ if ($versionName -ne "null") {
 } else {
     $versionName = "";
 }
-if ($env:APPVEYOR_REPO_BRANCH -ne 'master') {
-	$branch = "-$env:APPVEYOR_REPO_BRANCH";
-} else {
+if ($masterBranches -contains $env:APPVEYOR_REPO_BRANCH) {
 	$branch = "";
+} else {
+	$branch = "-$env:APPVEYOR_REPO_BRANCH";
 }
 if ($env:APPVEYOR_PULL_REQUEST_NUMBER) {
 	$suffix = "-pr$env:APPVEYOR_PULL_REQUEST_NUMBER";