prevent to append _helper.d.ts on each run

Author: kazemihabib

dts-generator/src/main/java/com/telerik/dts/FileWriter.java

@@ -56,10 +56,10 @@ public void write(String content, String fileName) {
         }
     }
 
-    public void writeHelperTypings(String content) {
+    public void writeHelperTypings(String content, boolean append) {
         try {
                 String outFile = this.outDir.getAbsolutePath() + File.separator + "_helpers.d.ts";
-                this.ps = new PrintStream(new FileOutputStream(outFile, true));
+                this.ps = new PrintStream(new FileOutputStream(outFile, append));
 
                 this.ps.print(content);
                 this.ps.println();

dts-generator/src/main/java/com/telerik/dts/Generator.java

@@ -41,16 +41,18 @@ private void generateDts() {
     }
 
     private void writeHelperTypings() {
-
         List<String> helperTypings = new ArrayList<>();
         helperTypings.add("declare module native {\n" +
                 "\texport class Array<T> {\n" +
                 "\t\tpublic constructor();\n" +
                 "\t}\n" +
                 "}\n");
 
+        boolean append = false;
+        
         for (String helper : helperTypings) {
-            this.fw.writeHelperTypings(helper);
+            this.fw.writeHelperTypings(helper, append);
+            append = true;
         }
     }