DDC-3841: [GH-1470] [CI] Added dev requirement for "doctrine/coding-standard"

[doctrinebot]

Jira issue originally created by user @doctrinebot:

This issue is created automatically through a Github pull request on behalf of phansys:

Url: #1470

Message:

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

• Added dev requirement for doctrine/coding-standard.
• Updated Travis config in order to use the new requirement within
  before_script lifecycle.

[doctrinebot]

• relates to DDC-585: Create a coding standards document

[doctrinebot]

Comment created by phansys:

Take this as a probe of the current status of the Doctrine's CS. IMO, we should decide how to proceed in order to get a clean codebase, and I think we should apply some tool like PHP-CS-Fixer or update PHP_CodeSniffer to 2.0 in order to achieve the same feature.

Ping @Ocramius.

[doctrinebot]

Comment created by @Ocramius:

[~phansys] I already replied on the PR: needs CS changes before merging, and other PRs take priority first.

[doctrinebot]

Comment created by phansys:

[~Ocramius], auto CS fixes aren't available with PHP_CodeSniffer at 1.x version (they are in yet unreleased 2.x); that is why I created this PR #1460 using PHP-CS-fixer, while I've also added a rule for Doctrine's logical NOT CS: PHP-CS-Fixer/PHP-CS-Fixer#1303.
IMO, at some point we should use any of these tools to ensure all the CS rules are respected.

[Majkl578]

Done in 2be1b7d.