Fix problem with header names letter casing
merged branch camcima/master (PR #105)

This PR was merged into the master branch.

Discussion
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400 Bad Request - Invalid Headers

There's a problem with Goutte HTTP header naming when it uppercase only the first character of the header name, for instance, User-agent. Guzzle sets its own user agent header as "User-Agent" with both initial letters uppercased. When a request is made, instead of one header overwriting the other, both are snet to the web server. IIS, for instance, rejects the request: 400 Bad Request - Invalid Headers.

This one line fix makes the first character of all parts of the header name uppercased.

Commits
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a9f76dc Fix problem with header names letter casing