优化 sourcemaps 输出细节

gulpfile.js

@@ -56,7 +56,7 @@ const js = () => {
   }))
   .pipe(concat('layui.js', {newLine: ''}))
   .pipe(header.apply(null, config.comment))
-  .pipe(sourcemaps.write(''))
+  .pipe(sourcemaps.write('.'))
   .pipe(gulp.dest(dest));
 };
 
@@ -71,7 +71,7 @@ const css = () => {
     compatibility: 'ie8'
   }))
   .pipe(concat('layui.css', {newLine: ''}))
-  .pipe(sourcemaps.write(''))
+  .pipe(sourcemaps.write('.'))
   .pipe(gulp.dest(dest +'/css'));
 };