minor #653 Add validation of the composer files on Travis (stof, javiereguiluz)

This PR was merged into the master branch.

Discussion
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Add validation of the composer files on Travis

This performs validation of the composer metadata to ensure they are valid:

- composer.json does not contain any error
- composer.json does not trigger any warning (thanks to the strict mode)
- composer.lock is uptodate

Commits
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5deb547 Minor change to make things consistent
2493692 Update lock file for the move of deps to dev deps
99246aa Add validation of the composer files on Travis

Author: javiereguiluz

.travis.yml

@@ -29,3 +29,5 @@ script:
   - ./bin/console lint:xliff translations
   # this checks that the application doesn't use dependencies with known security vulnerabilities
   - ./bin/console security:check --end-point=http://security.sensiolabs.org/check_lock
+  # this checks that the composer.json and composer.lock files are valid
+  - composer validate --strict