Use monotonic clock

* Uses Process.clock_gettime(Process::CLOCK_MONOTONIC), which was added in Ruby 2.1, instead of Time.now.
  This prevents issues with scheduled timers when running alongside Timecop as reported in
  iconara#52
* Bumps minimum Ruby version to 2.1
* Updates Travis test ruby versions

.travis.yml

@@ -6,9 +6,13 @@ bundler_args: --without development
 services:
   - redis-server
 rvm:
-  - 1.9.3
-  - 2.0.0
-  - 2.1.1
+  - 2.1.10
+  - 2.2.10
+  - 2.3.8
+  - 2.4.10
+  - 2.5.9
+  - 2.6.8
+  - 2.7.4
   - jruby
   - jruby-head
   - rbx-2

ione.gemspec

@@ -20,5 +20,5 @@ Gem::Specification.new do |s|
   s.require_paths = %w(lib)
 
   s.platform = Gem::Platform::RUBY
-  s.required_ruby_version = '>= 1.9.3'
+  s.required_ruby_version = '>= 2.1.0'
 end

lib/ione/io/io_reactor.rb

@@ -92,7 +92,7 @@ class IoReactor
       # @param options [Hash] only used to inject behaviour during tests
       def initialize(options={})
         @options = options
-        @clock = options[:clock] || Time
+        @clock = options[:clock] || MonotonicClock
         @state = PENDING_STATE
         @error_listeners = []
         @unblocker = Unblocker.new
@@ -464,7 +464,7 @@ def to_s
     class IoLoopBody
       def initialize(unblocker, options={})
         @selector = options[:selector] || IO
-        @clock = options[:clock] || Time
+        @clock = options[:clock] || MonotonicClock
         @timeout = options[:tick_resolution] || 1
         @drain_timeout = options[:drain_timeout] || 5
         @lock = Mutex.new
@@ -540,7 +540,7 @@ def to_s
     # @private
     class Scheduler
       def initialize(options={})
-        @clock = options[:clock] || Time
+        @clock = options[:clock] || MonotonicClock
         @lock = Mutex.new
         @timer_queue = Heap.new
         @pending_timers = {}
@@ -615,5 +615,12 @@ def to_s
         %(#<#{self.class.name} @timers=[#{@pending_timers.values.map(&:to_s).join(', ')}]>)
       end
     end
+
+    # @private
+    module MonotonicClock
+      def self.now
+        Process.clock_gettime(Process::CLOCK_MONOTONIC)
+      end
+    end
   end
 end