minor #19080 Fixed typo in PHPDoc (ThomasLandauer)

This PR was merged into the 2.7 branch.

Discussion
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Fixed typo in PHPDoc

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes/no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes/no
| Fixed tickets | comma-separated list of tickets fixed by the PR, if any
| License       | MIT
| Doc PR        | reference to the documentation PR, if any

Commits
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9e7b347 Fixed typo in PHPDoc

Author: fabpot

src/Symfony/Component/HttpFoundation/File/File.php

@@ -68,7 +68,7 @@ public function guessExtension()
      * mime_content_type() and the system binary "file" (in this order), depending on
      * which of those are available.
      *
-     * @return string|null The guessed mime type (i.e. "application/pdf")
+     * @return string|null The guessed mime type (e.g. "application/pdf")
      *
      * @see MimeTypeGuesser
      */