minor #18980 [BrowserKit] Bump the dom-crawler minimum version requirement (jakzal)

This PR was submitted for the 2.3 branch but it was merged into the 2.7 branch instead (closes #18980).

Discussion
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[BrowserKit] Bump the dom-crawler minimum version requirement

| Q             | A
| ------------- | ---
| Branch?       | 2.3
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #18826
| License       | MIT
| Doc PR        | -

The BrowserKit Client will not work with DomCrawler 2.0 if the CssSelector component is not installed.

This will require an amendment when merging into the 2.8 branch. It currently uses `~2.0,>=2.0.5|~3.0.0`, while it should be `~2.1|~3.0.0`.

Commits
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5579d86 [BrowserKit] Bump dom-crawler minimum version requirement

src/Symfony/Component/BrowserKit/composer.json

@@ -17,7 +17,7 @@
     ],
     "require": {
         "php": ">=5.3.9",
-        "symfony/dom-crawler": "~2.0,>=2.0.5"
+        "symfony/dom-crawler": "~2.1"
     },
     "require-dev": {
         "symfony/process": "~2.3.34|~2.7,>=2.7.6",