Fix the fixed style error that broke platform iteration

Author: ianfixes

CHANGELOG.md

@@ -20,6 +20,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 - Example sketches with no configured platforms were printing the wrong configuration values to the debug message
 - Libraries directory was not being automatically created prior to attempting to change directory into it
+- A style error whose "fix" caused an _actual_ error.
 
 ### Security
 

exe/arduino_ci.rb

@@ -373,7 +373,7 @@ def choose_platform_set(config, reason, desired_platforms, library_properties)
     # completely ignore default config, opting for brute-force library matches
     # OTOH, we don't need to assure platforms because we defined them
     return inform_multiline("Default config, platforms matching architectures in library.properties") do
-      supported_platforms.each_key do |p|
+      supported_platforms.keys.each do |p|  # rubocop:disable Style/HashEachMethods
         puts "    #{p}"
       end # this returns supported_platforms
     end