Extract _prependChangelog() method

index.js

@@ -163,14 +163,19 @@ module.exports = class LernaChangelogGeneratorPlugin extends Plugin {
       this.log.log(`! Prepending ${infile} with release notes.`);
     } else {
       let currentFileData = hasInfile ? fs.readFileSync(infile, { encoding: 'utf8' }) : '';
-      fs.writeFileSync(infile, changelog + EOL + EOL + currentFileData, { encoding: 'utf8' });
+      let newContent = this._insertContent(changelog, currentFileData);
+      fs.writeFileSync(infile, newContent, { encoding: 'utf8' });
     }
 
     if (!hasInfile) {
       await this.exec(`git add ${infile}`);
     }
   }
 
+  _insertContent(newContent, oldContent) {
+    return newContent + EOL + EOL + oldContent;
+  }
+
   async beforeRelease() {
     let processedChangelog = await this.processChangelog();