Fixed the syntax of a composer.json file
minor #12783 Fixed the syntax of a composer.json file (GrahamCampbell)

This PR was merged into the 2.3 branch.

Discussion
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Fixed the syntax of a composer.json file

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | N/A

##### This pull request fixes the syntax of a composer.json file.

There should not be a space before a colon following a double quote. This is not bad syntax, but it just an inconsistency.

Commits
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0f8547a Fixed the syntax of a composer.json file