When I run...
composer global require drush/drush:dev-master
...I get...
Your requirements could not be resolved to an installable set of packages.
Problem 1
- Can only install one of: consolidation/output-formatters[3.1.12, 2.1.3].
- Can only install one of: consolidation/output-formatters[3.1.12, 2.1.3].
- Can only install one of: consolidation/output-formatters[3.1.12, 2.1.3].
- drush/drush dev-master requires consolidation/output-formatters ^3.1.12 -> satisfiable by consolidation/output-formatters[3.1.12].
- Installation request for drush/drush dev-master -> satisfiable by drush/drush[dev-master].
- Installation request for consolidation/output-formatters (locked at 2.1.3) -> satisfiable by consolidation/output-formatters[2.1.3].
My PHP version is 5.6.11.