fix small typo on 'lib/concurrent': one -> on

Author: rubemz

lib/concurrent.rb

@@ -45,7 +45,7 @@
 
 # @!macro [new] monotonic_clock_warning
 #
-#   @note Time calculations one all platforms and languages are sensitive to
+#   @note Time calculations on all platforms and languages are sensitive to
 #     changes to the system clock. To alleviate the potential problems
 #     associated with changing the system clock while an application is running,
 #     most modern operating systems provide a monotonic clock that operates
@@ -129,4 +129,4 @@
 # * Exclude features that don't make sense in Ruby
 # * Be small, lean, and loosely coupled
 module Concurrent
-end
+end