minor symfony#23859 [DomCrawler] Fix testHtml method with regexp (MatthieuMota)

This PR was submitted for the master branch but it was merged into the 2.7 branch instead (closes symfony#23859).

Discussion
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[DomCrawler] Fix testHtml method with regexp

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | symfony#23858
| License       | MIT
| Doc PR        | no

As explained in this issue symfony#23858, adding a regexp in addition to the trim for the testHtml method of [CrawlerTest](https://github.com/symfony/symfony/blob/master/src/Symfony/Component/DomCrawler/Tests/CrawlerTest.php#L397) class.

Commits
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339592d Fix testHtml method with regexp

Author: nicolas-grekas

src/Symfony/Component/DomCrawler/Tests/CrawlerTest.php

@@ -353,7 +353,7 @@ public function testText()
     public function testHtml()
     {
         $this->assertEquals('<img alt="Bar">', $this->createTestCrawler()->filterXPath('//a[5]')->html());
-        $this->assertEquals('<input type="text" value="TextValue" name="TextName"><input type="submit" value="FooValue" name="FooName" id="FooId"><input type="button" value="BarValue" name="BarName" id="BarId"><button value="ButtonValue" name="ButtonName" id="ButtonId"></button>', trim($this->createTestCrawler()->filterXPath('//form[@id="FooFormId"]')->html()));
+        $this->assertEquals('<input type="text" value="TextValue" name="TextName"><input type="submit" value="FooValue" name="FooName" id="FooId"><input type="button" value="BarValue" name="BarName" id="BarId"><button value="ButtonValue" name="ButtonName" id="ButtonId"></button>', trim(preg_replace('~>\s+<~', '><', $this->createTestCrawler()->filterXPath('//form[@id="FooFormId"]')->html())));
 
         try {
             $this->createTestCrawler()->filterXPath('//ol')->html();