modernise the development environment a bit (Guzzle 3)

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[burhan@enceladus guzzle-jsonrpc (docker-g-3)] {0} $ make deps
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Installation request for doctrine/instantiator 1.1.0 -> satisfiable by doctrine/instantiator[1.1.0].
    - doctrine/instantiator 1.1.0 requires php ^7.1 -> your PHP version (5.6.31) does not satisfy that requirement.
  Problem 2
    - Installation request for phpunit/phpunit 4.8.36 -> satisfiable by phpunit/phpunit[4.8.36].
    - phpunit/phpunit 4.8.36 requires ext-dom * -> the requested PHP extension dom is missing from your system.
  Problem 3
    - doctrine/instantiator 1.1.0 requires php ^7.1 -> your PHP version (5.6.31) does not satisfy that requirement.
    - phpunit/phpunit-mock-objects 2.3.8 requires doctrine/instantiator ^1.0.2 -> satisfiable by doctrine/instantiator[1.1.0].
    - Installation request for phpunit/phpunit-mock-objects 2.3.8 -> satisfiable by phpunit/phpunit-mock-objects[2.3.8].

  To enable extensions, verify that they are enabled in your .ini files:
    - /etc/php5/php.ini
    - /etc/php5/conf.d/bz2.ini
    - /etc/php5/conf.d/ctype.ini
    - /etc/php5/conf.d/curl.ini
    - /etc/php5/conf.d/iconv.ini
    - /etc/php5/conf.d/json.ini
    - /etc/php5/conf.d/openssl.ini
    - /etc/php5/conf.d/phar.ini
    - /etc/php5/conf.d/posix.ini
    - /etc/php5/conf.d/zlib.ini
  You can also run `php --ini` inside terminal to see which files are used by PHP in CLI mode.
make: *** [deps] Error 2
graze / guzzle-jsonrpc

modernise the development environment a bit (Guzzle 3) #33
