Fix Host reference in test runner script

Author: ianfixes

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Removed
 
 ### Fixed
+- Improper reference to `Host` in `arduino_ci.rb` test runner is now properly qualified
 
 ### Security
 

exe/arduino_ci.rb

@@ -157,7 +157,7 @@ def file_is_hidden_somewhere?(path)
 # print out some files
 def display_files(pathname)
   # `find` doesn't follow symlinks, so we should instead
-  realpath = Host.symlink?(pathname) ? Host.readlink(pathname) : pathname
+  realpath = ArduinoCI::Host.symlink?(pathname) ? ArduinoCI::Host.readlink(pathname) : pathname
 
   # suppress directories and dotfile-based things
   all_files = realpath.find.select(&:file?)