Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires guzzlehttp/guzzle 6.2 -> satisfiable by guzzlehttp/guzzle[6.2.0]. - guzzlehttp/guzzle 6.2.0 requires guzzlehttp/psr7 ~1.1 -> found guzzlehttp/psr7[1.1.0, ..., 1.9.x-dev] but it conflicts with your root composer.json require (^2.0). Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.

Process completed with exit code 2.