Fix confusing example

Remove useless and confusing `return` statement in "function argument" example.
cf. 'ignores the return value': `test/rename.spec.js:156`

README.md

@@ -25,7 +25,6 @@ gulp.src("./src/**/hello.txt")
     path.dirname += "/ciao";
     path.basename += "-goodbye";
     path.extname = ".md";
-    return path;
   }))
   .pipe(gulp.dest("./dist")); // ./dist/main/text/ciao/hello-goodbye.md