Fix issue where getSemanticDiagnostics was returning undefined on a .d.ts file.

src/services/services.ts

@@ -2389,7 +2389,7 @@ module ts {
 
             // If '-d' is enabled, check for emitter error. One example of emitter error is export class implements non-export interface
             let declarationDiagnostics = program.getDeclarationDiagnostics(targetSourceFile);
-            return semanticDiagnostics.concat(declarationDiagnostics);
+            return concatenate(semanticDiagnostics, declarationDiagnostics);
         }
 
         function getCompilerOptionsDiagnostics() {