Fixed the bug "dts files are emitted in a wrong folder"

index.ts

@@ -496,7 +496,7 @@ function ensureTypeScriptInstance(loaderOptions: LoaderOptions, loader: any): {
                 let output = languageService.getEmitOutput(filePath);
                 let declarationFile = output.outputFiles.filter(filePath => !!filePath.name.match(/\.d.ts$/)).pop();
                 if (declarationFile) {
-                    let assetPath = path.relative(process.cwd(), declarationFile.name);
+                    let assetPath = path.relative(compilation.compiler.context, declarationFile.name);
                     compilation.assets[assetPath] = {
                         source: () => declarationFile.text,
                         size: () => declarationFile.text.length

test/comparison-tests/declarationOutput/expectedOutput-2.0/output.txt

@@ -1,7 +1,7 @@
-                               Asset       Size  Chunks             Chunk Names
-                           bundle.js    2.19 kB       0  [emitted]  main
-    .test/declarationOutput/app.d.ts  110 bytes          [emitted]  
-.test/declarationOutput/sub/dep.d.ts   63 bytes          [emitted]  
+       Asset       Size  Chunks             Chunk Names
+   bundle.js    2.19 kB       0  [emitted]  main
+    app.d.ts  110 bytes          [emitted]  
+sub/dep.d.ts   63 bytes          [emitted]  
 chunk    {0} bundle.js (main) 703 bytes [rendered]
     [0] ./.test/declarationOutput/app.ts 535 bytes {0} [built]
     [1] ./.test/declarationOutput/sub/dep.ts 168 bytes {0} [built]