Fix 'require' statement in docs

Author: vvasilev-

README.md

@@ -21,7 +21,7 @@
 ```javascript
 var fs = require('fs');
 var postcss = require('postcss');
-var sprites = require('postcss-sprites').default; // Babel@6 drops support for CommonJS interop
+var sprites = require('postcss-sprites');
 
 var css = fs.readFileSync('./css/style.css', 'utf8');
 var opts = {

examples/filter-by.md

@@ -10,7 +10,7 @@
 
 ```javascript
 var postcss = require('postcss');
-var sprites = require('postcss-sprites').default;
+var sprites = require('postcss-sprites');
 var opts = {
 	stylesheetPath: './css',
 	spritePath: './css/images/',

examples/group-by.md

@@ -12,7 +12,7 @@
 
 ```javascript
 var postcss = require('postcss');
-var sprites = require('postcss-sprites').default;
+var sprites = require('postcss-sprites');
 var opts = {
 	stylesheetPath: './css',
 	spritePath: './css/images/',

examples/output-dimensions.md

@@ -10,8 +10,8 @@
 
 ```javascript
 var postcss = require('postcss');
-var sprites = require('postcss-sprites').default;
-var updateRule = require('postcss-sprites').updateRule;
+var sprites = require('postcss-sprites');
+var updateRule = require('postcss-sprites/lib/core').updateRule;
 var opts = {
 	stylesheetPath: './css',
 	spritePath: './css/images/',

examples/relative-to-rule.md

@@ -16,7 +16,7 @@
 
 ```javascript
 var postcss = require('postcss');
-var sprites = require('postcss-sprites').default;
+var sprites = require('postcss-sprites');
 var opts = {
 	stylesheetPath: './css',
 	spritePath: './css/images/',

examples/responsive-spritesheets.md

@@ -10,7 +10,7 @@
 
 ```javascript
 var postcss = require('postcss');
-var sprites = require('postcss-sprites').default;
+var sprites = require('postcss-sprites');
 var opts = {
 	stylesheetPath: './css',
 	spritePath: './css/images/',

examples/skip-prefix.md

@@ -11,7 +11,7 @@
 ```javascript
 var path = require('path');
 var postcss = require('postcss');
-var sprites = require('postcss-sprites').default;
+var sprites = require('postcss-sprites');
 var opts = {
 	stylesheetPath: './css',
 	spritePath: './css/images/',