Fix all the things

lib/stub-generator.js

@@ -76,13 +76,18 @@ StubGenerator.prototype.build = function() {
 
         var content = fs.readFileSync(fullInputPath, 'UTF8');
         var imports = importsFor(content, fullInputPath);
+        var needsImportsReWritten = false;
 
         Object.keys(imports).forEach(function(name) {
+          needsImportsReWritten = true;
           imports[name].version = versionForModuleName(name, this.basedir);
         }, this);
 
-        // TODO: only add files that required rewriting
-        fs.writeFileSync(fullOutputPath, rewriteImports(content, imports));
+        if (needsImportsReWritten) {
+          fs.writeFileSync(fullOutputPath, rewriteImports(content, imports));
+        } else {
+          fs.writeFileSync(fullOutputPath, content);
+        }
 
         this.stubs.set(fullInputPath, imports);